If you close the external circuit of a charged battery, an electric current will appear. In this case, the following reactions take place:

at the negative plate

at the positive plate

where e - the charge of an electron is

For every two molecules of acid consumed, four water molecules are formed, but at the same time two water molecules are consumed. Therefore, in the end, only two water molecules are formed. Adding equations (27.1) and (27.2), we obtain the final discharge reaction:

Equations (27.1) - (27.3) should be read from left to right.

When the battery is discharged, lead sulfate is formed on the plates of both polarities. Sulfuric acid is consumed at both the positive and negative plates, while the positive plates consume more acid than the negative ones. At the positive plates, two water molecules are formed. The electrolyte concentration decreases when the battery is discharged, while it decreases to a greater extent at the positive plates.

If you change the direction of the current through the battery, then the direction of the chemical reaction will be reversed. The battery charging process will begin. The charge reactions at the negative and positive plates can be represented by equations (27.1) and (27.2), and the total reaction can be represented by equation (27.3). These equations should now be read from right to left. When charging, lead sulfate at the positive plate is reduced to lead peroxide, at the negative plate - into metallic lead. In this case, sulfuric acid is formed and the concentration of the electrolyte increases.

The electromotive force and voltage of the battery depend on many factors, of which the most important are the acid content in the electrolyte, temperature, current and its direction, and the degree of charge. The relationship between electromotive force, voltage and current can be written

san as follows:

at discharge

where E 0 - reversible EMF; E p - EMF of polarization; R - internal resistance of the battery.

Reversible EMF is the EMF of an ideal battery, in which all types of losses are eliminated. In such a battery, the energy received during charging is fully returned when discharging. The reversible EMF depends only on the acid content in the electrolyte and temperature. It can be determined analytically from the heat of formation of the reactants.

A real battery is in conditions close to ideal if the current is negligible and the duration of its passage is also short. Such conditions can be created by balancing the battery voltage with some external voltage (voltage standard) using a sensitive potentiometer. The voltage measured in this way is called the open circuit voltage. It is close to the reversible emf. In table. 27.1 shows the values ​​of this voltage, corresponding to the density of the electrolyte from 1.100 to 1.300 (refer to a temperature of 15 ° C) and a temperature of 5 to 30 ° C.

As can be seen from the table, at an electrolyte density of 1.200, which is common for stationary batteries, and a temperature of 25 ° C, the battery voltage with an open circuit is 2.046 V. During the discharge, the density of the electrolyte decreases slightly. The corresponding voltage drop in an open circuit is only a few hundredths of a volt. The change in open circuit voltage due to temperature change is negligible and is of more theoretical interest.

If a certain current passes through the battery in the direction of charge or discharge, the battery voltage changes due to an internal voltage drop and a change in EMF caused by side chemical and physical processes at the electrodes and in the electrolyte. The change in the EMF of the battery, caused by these irreversible processes, is called polarization. The main causes of polarization in the battery are the change in the electrolyte concentration in the pores of the active mass of the plates in relation to its concentration in the rest of the volume and the resulting change in the concentration of lead ions. When discharged, acid is consumed, when charged, it is formed. The reaction takes place in the pores of the active mass of the plates, and the influx or removal of acid molecules and ions occurs through diffusion. The latter can take place only if there is a certain difference in electrolyte concentrations in the region of the electrodes and in the rest of the volume, which is set in accordance with the current and temperature, which determines the viscosity of the electrolyte. A change in the electrolyte concentration in the pores of the active mass causes a change in the concentration of lead ions and EMF. During discharge, due to a decrease in the electrolyte concentration in the pores, the EMF decreases, and during charging, due to an increase in the electrolyte concentration, the EMF increases.

The electromotive force of polarization is always directed towards the current. It depends on the porosity of the plates, current and

temperature. The sum of the reversible EMF and the polarization EMF, i.e. E 0 ± E P , represents the EMF of the battery under current or dynamic EMF. When discharged, it is less than the reversible emf, and when charged, it is greater. The battery voltage under current differs from the dynamic EMF only by the value of the internal voltage drop, which is relatively small. Therefore, the voltage of an energized battery also depends on current and temperature. The influence of the latter on the battery voltage during discharge and charge is much greater than with an open circuit.

If the battery circuit is opened while discharging, the battery voltage will slowly increase to the open circuit voltage due to continued diffusion of the electrolyte. If you open the battery circuit while charging, the battery voltage will slowly decrease to the open circuit voltage.

The inequality of electrolyte concentrations in the area of ​​the electrodes and in the rest of the volume distinguishes the operation of a real battery from an ideal one. When charging, the battery behaves as if it contained a very dilute electrolyte, and when charged, it behaves as if it contains a very concentrated one. A dilute electrolyte is constantly mixed with a more concentrated one, while a certain amount of energy is released in the form of heat, which, provided that the concentrations are equal, could be used. As a result, the energy given off by the battery during discharge is less than the energy received during charging. Energy loss occurs due to the imperfection of the chemical process. This type of loss is the main one in the battery.

Battery internal resistanceTorah. The internal resistance is made up of the resistances of the plate frame, active mass, separators and electrolyte. The latter accounts for most of the internal resistance. The resistance of the battery increases during discharge and decreases during charging, which is a consequence of changes in the concentration of the solution and the content of sulphate.

veil in the active mass. The resistance of the battery is small and noticeable only at a large discharge current, when the internal voltage drop reaches one or two tenths of a volt.

Battery self-discharge. Self-discharge is the continuous loss of chemical energy stored in the battery due to side reactions on the plates of both polarities, caused by accidental harmful impurities in the materials used or impurities introduced into the electrolyte during operation. Of greatest practical importance is self-discharge caused by the presence in the electrolyte of various metal compounds that are more electropositive than lead, such as copper, antimony, etc. Metals are released on negative plates and form many short-circuited elements with lead plates. As a result of the reaction, lead sulfate and hydrogen are formed, which is released on the contaminated metal. Self-discharge can be detected by slight outgassing at the negative plates.

On the positive plates, self-discharge also occurs due to the normal reaction between base lead, lead peroxide and electrolyte, which results in the formation of lead sulfate.

Self-discharge of the battery always occurs: both with an open circuit, and with discharge and charge. It depends on the temperature and density of the electrolyte (Fig. 27.2), and with an increase in the temperature and density of the electrolyte, self-discharge increases (the loss of charge at a temperature of 25 ° C and an electrolyte density of 1.28 is taken as 100%). The capacity loss of a new battery due to self-discharge is about 0.3% per day. As the battery ages, self-discharge increases.

Abnormal plate sulfation. Lead sulfate is formed on plates of both polarities with each discharge, as can be seen from the discharge reaction equation. This sulfate has

fine crystalline structure and charging current is easily restored into lead metal and lead peroxide on plates of the appropriate polarity. Therefore, sulfation in this sense is a normal phenomenon that is an integral part of battery operation. Abnormal sulfation occurs when batteries are over-discharged, systematically undercharged, or left in a discharged state and inactive for long periods of time, or when they are operated at excessively high electrolyte density and at high temperatures. Under these conditions, fine crystalline sulfate becomes denser, crystals grow, greatly expanding the active mass, and are difficult to recover when charged due to high resistance. If the battery is inactive, temperature fluctuations contribute to the formation of sulfate. As the temperature rises, small sulfate crystals dissolve, and as the temperature decreases, the sulfate slowly crystallizes out and the crystals grow. As a result of temperature fluctuations, large crystals are formed at the expense of small ones.

In sulfated plates, the pores are clogged with sulfate, the active material is squeezed out of the grids, and the plates often warp. The surface of sulfated plates becomes hard, rough, and when rubbed

The material of the plates between the fingers feels like sand. The dark brown positive plates become lighter and white sulfate spots appear on the surface. Negative plates become hard, yellowish gray. The capacity of the sulfated battery is reduced.

Beginning sulfation can be eliminated by a long charge with a light current. With strong sulfation, special measures are necessary to bring the plates back to normal.

Page 2 of 26

1.3. Basic electrical characteristics of batteries

Electromotive force and voltage . Electromotive force (EMF) is the potential difference between the positive and negative electrodes of the battery when the external circuit is open.
The magnitude of the emf depends mainly on the electrode potentials, i.e., on the physical and chemical properties of the substances from which the plates and electrolyte are made, but does not depend on the size of the battery plates.
The EMF of an acid battery also depends on the density of the electrolyte. It has been theoretically and practically established that the EMF of a battery with sufficient accuracy for practice can be determined by the formula
E=0.85 + g,
where g is the electrolyte density at 15°С, g/cm3 .
For acid starter batteries, in which the electrolyte density ranges from 1.12 to 1.29 g / cm 3 , EMF changes accordingly from 1.97 to 2.14 V .
It is almost impossible to measure EMF with absolute accuracy. However, for practical purposes, the EMF can be approximately and fairly accurately measured with a voltmeter having a high internal resistance (at least 1000 ohms per 1 V). In this case, a small amount of current will pass through the voltmeter.
The battery voltage is the potential difference between the positive and negative plates with a closed external circuit, which includes any current consumer, that is, when current passes through the battery. In this case, the readings of the voltmeter when measuring voltage will always be less than when measuring EMF, and this difference will be the greater, the more current passes through the battery.
EMF and voltage depend on a number of factors. The emf varies with the density and temperature of the electrolyte. The voltage, in turn, depends on the EMF, the magnitude of the discharge current (load) and the internal resistance of the battery.
The dependence of the battery EMF on the density of the electrolyte (concentration of the H2SO4 solution) is given below:

Electrolyte density at 25°С,
g/cm 3 .................................... 1.05 1.10 1.15 1 .20 1.25 1.28 1.30
H2SO4, %....................... 7.44 14.72 21.68 27.68 33.8 37.4 39.7
Battery EMF, V.......... 1.906 1.960 2.005 2.048 2.095 2.125 2.144
From this dependence it can be seen that with an increase in the concentration of sulfuric acid, the EMF also increases. From this, however, it does not follow that in order to obtain a greater EMF, one can excessively increase the density of the electrolyte. It has been established that starter batteries work quite well when the density of the electrolyte in them is 1.27 - 1.29 g / cm 3. In addition, the electrolyte with a density of 1.29 g / cm 3 has the lowest freezing point.
When the temperature of the electrolyte changes, the EMF of the battery also changes. So, with a change in the electrolyte temperature from +20 ° C to -40 ° C, the battery EMF decreases from 2.12 to 2.096 V. To a much greater extent, with a change in the temperature of the electrolyte, the voltage changes, since it depends not only on the EMF, but also on the internal resistance of the battery, which increases significantly with decreasing temperature.
Between the EMF, voltage, internal resistance and the magnitude of the discharge current, there is the following relationship:
U=E-Ir,
where U- voltage;
E- e. d.s. battery;
I is the value of the discharge current;
r is the internal resistance of the battery.
From this formula it can be seen that at a constant value of the EMF, measured with an open circuit, the battery voltage drops as the current given off during the discharge process increases.
internal resistance. The internal resistance of the battery is relatively small, but in cases where the battery is discharged by a large current, for example, when starting the engine with a starter, the internal resistance of each battery is very significant.
Internal resistance is the sum of the resistance of the electrolyte, separators and plates. The main component is the resistance of the electrolyte, which changes with temperature and sulfuric acid concentration.
The dependence of the specific resistance of an electrolyte with a density of 1.30 g / cm 3 on temperature is shown below:

Temperature, °С Resistivity of electrolyte Ohm cm
+ 40 0,89
+ 25 1,28
+ 18 1,46
0 1,92
– 18 2,39
As can be seen from the above data, with a decrease in the temperature of the electrolyte from +40°C to -18°C, the resistivity increases by 2.7 times. The lowest value of resistivity has an electrolyte with a density of 1.223 g/cm 3 at 15°C (30% H2SO4 solution by weight).
The second component of the resistance in the battery is the resistance of the separators. It depends mainly on their porosity. Separators are made of an electrically insulating material, the pores of which are filled with electrolyte, which determines the electrical conductivity of the separator.
In this regard, one could assume that with a change in temperature, the resistance of the separator will change in the same proportion as the resistance of the electrolyte, but this is not entirely true. Some types of separators, for example, separators made of microporous ebonite (mipore) are not sensitive to temperature changes.
The third factor included in the total amount of internal resistance of the element is the active mass and the grids of positive and negative plates.
The resistance of lead sponge negative plate differs slightly from the resistance of the grating material, while the lead peroxide positive plate resistance exceeds the grating resistance by 10,000 times. Unlike the resistance of an electrolyte, the lattice resistance decreases with decreasing temperature. But in view of the fact that the resistance of the electrolyte is many times greater than the resistance of the plates, the decrease in their resistance with decreasing temperature very slightly compensates for the overall decrease in the resistance of the electrolyte.
The resistance of the plates is affected by the degree of charge of the battery. During the discharge process, the resistance of the plates increases, since the lead sulfate formed on the positive and negative plates almost does not conduct electricity.
Compared with other types of batteries, acid batteries have a relatively low internal resistance, which determines their widespread use as starter batteries in motor vehicles.
Capacity. The capacity of a battery is the amount of electricity that a fully charged battery can deliver at a given discharge mode, temperature, and final voltage. Capacitance is measured in ampere-hours and is determined by the formula
c=ipp,
where WITH– capacity, Ah ;
IP is the strength of the discharge current, and ;
tp– discharge time, h .
The battery capacity value is mainly determined by the following factors: discharge mode (discharge current), electrolyte concentration and temperature. Batteries with forced discharge modes give less capacity than when discharged with longer modes (small current).
The decrease in capacitance under forced discharge modes occurs for the following reasons.
During the discharge, the transformation of the active mass of the plates into lead sulfate occurs not only on the surface of the plates, but also inside them. If the discharge is carried out with a low current and slowly, then the electrolyte has time to penetrate into the deep layers of the active mass, and the water formed as a result of the reaction in the pores has time to mix with the bulk of the electrolyte. Under forced discharge modes, the concentration of sulfuric acid in the electrolyte inside the plates is significantly reduced, the fresh electrolyte does not have time to penetrate deep into the active mass, the reaction proceeds mainly on the surface of the plates, since the pores are clogged and the underlying layers of the active mass almost do not take part in the reaction. At the same time, as a result of a significant increase in the internal resistance of the battery, the voltage at its terminals drops sharply.
However, after the battery has been discharged in boost mode, it can be discharged again after a short break. This serves as a clear confirmation that the decrease in capacity in the battery when discharging with a large amount of current occurs as a result of incomplete use of the active mass of the plates.
In addition to the magnitude of the discharge current, the battery capacity is significantly affected by the concentration of the electrolyte, which determines the potential of the plates, the electrical resistance of the electrolyte and its viscosity, which in turn affects the ability of the electrolyte to penetrate into the deep layers of the active mass of the plates.
During the discharge, the density of the electrolyte decreases and at the end of the discharge, an insufficient amount of acid enters the active mass of the plates, as a result of which the battery voltage drops and its further discharge becomes impossible. The greater the difference between the concentrations of the electrolyte outside the plates and the electrolyte in the pores of the active mass, the more intense the process of acid penetration into the pores of the plates. In this regard, the use of an electrolyte with a higher density, it would seem, should increase the capacity. But in reality, an excessively high density does not lead to an increase in capacity, since an increase in electrolyte density inevitably leads to an increase in the viscosity of the electrolyte, as a result of which the process of electrolyte penetration into the depth of the active mass of the plates worsens, and the voltage at the battery terminals drops.
It has been established that the storage battery with an electrolyte density of 1.27 - 1.29 g/cm 3 has the highest capacity.
The battery capacity also depends on temperature. As the temperature decreases, the capacitance decreases, and as the temperature rises, it increases. This is explained by the fact that with decreasing temperature, the viscosity of the electrolyte increases, as a result of which it enters the plates in insufficient quantities.
The values ​​of the viscosity of the electrolyte with a density of 1.223 g / cm 3 depending on the temperature are given below:
Temperature, °C........... +30 +25 +20 +10 0 - 10 - 20 - 30
Absolute viscosity,
pz(poise)....................... 1.596 1.784 2.006 2.600 3.520 4.950 7.490 12.200
The capacitance of the positive and negative plates does not change to the same extent with temperature changes. If at ordinary temperature the capacitance of the element is limited by positive plates, then at low temperatures it is negative, since as the temperature decreases, the capacitance of the negative plate decreases to a much greater extent than the positive one.
Recently, the capacity of rechargeable batteries at low temperatures has been significantly increased through the use of thinner synthetic separators with high porosity (up to 80%) and additives, the so-called dilators, to the active mass of negative plates, which give it greater porosity.
In addition to the discharge mode, electrolyte concentration and temperature, the battery capacity depends on its service life, on the storage period during which the battery has been inactive, on the presence of harmful impurities, etc. The capacity of a new battery entering operation for the first time (during warranty period) rises, as the plates are formed, after which it remains constant for a certain period and then begins to gradually fall. The loss of battery capacity at the end of its service life is explained by a decrease in the porosity of the negative plates and the loss of the active mass of the positive plates.
If a charged battery has been inactive for a long time, then when it is discharged, the given capacity will be significantly less. This is due to the natural phenomenon of self-discharge when the battery is idle.

Is it possible to accurately judge the degree of charge of the battery by the EMF?

The electromotive force (EMF) of a battery is the difference in its electrode potentials, measured with an open external circuit:

Е = φ+ – φ–

where φ+ and φ– are, respectively, the potentials of the positive and negative electrodes with an open external circuit.

EMF of a battery consisting of n series-connected batteries:

In turn, the electrode potential in an open circuit generally consists of the equilibrium electrode potential, which characterizes the equilibrium (stationary) state of the electrode (in the absence of transient processes in the electrochemical system), and the polarization potential.

This potential is generally defined as the difference between the potential of the electrode during discharge or charge and its potential in the equilibrium state in the absence of current. However, it should be noted that the state of the battery immediately after turning off the charging or discharging current is not equilibrium due to the difference in the electrolyte concentration in the pores of the electrodes and the interelectrode space. Therefore, the electrode polarization remains in the battery for quite a long time even after the charging or discharging current is turned off and characterizes in this case the deviation of the electrode potential from the equilibrium value due to the transient process, that is, mainly due to diffusion equalization of the electrolyte concentration in the battery from the moment the external circuit is opened to the establishment equilibrium steady state in the battery.

The chemical activity of the reagents collected in the electrochemical system of the battery, and, consequently, the change in the EMF of the battery is very slightly dependent on temperature. When the temperature changes from -30°C to +50°C (in the operating range for the battery), the electromotive force of each battery in the battery changes by only 0.04 V and can be neglected during battery operation.

With an increase in the density of the electrolyte, the EMF increases. At a temperature of + 18 ° C and a density of 1.28 g / cm3, the battery (meaning one can) has an EMF of 2.12 V. A six-cell battery has an EMF of 12.72 V (6 × 2.12 V \u003d 12 .72 V).

By EMF it is impossible to accurately judge the degree of charge of the battery.
The EMF of a discharged battery with a higher electrolyte density will be higher than the EMF of a charged battery, but with a lower electrolyte density. The value of the EMF of a healthy battery depends on the density of the electrolyte (its degree of charge) and varies from 1.92 to 2.15 V.

During the operation of batteries, by measuring the EMF, a serious malfunction of the battery can be detected (short circuit of the plates in one or more banks, breakage of the connecting conductors between the banks, etc.).

EMF is measured with a high-resistance voltmeter (internal resistance of the voltmeter is not less than 300 Ohm / V). During the measurements, the voltmeter is connected to the terminals of the battery or battery. In this case, no charging or discharging current must flow through the accumulator (battery)!

***
Electromotive force (EMF) is a scalar physical quantity that characterizes the work of external forces, that is, any forces of non-electric origin acting in quasi-stationary DC or AC circuits.
EMF, like voltage, is measured in volts in the International System of Units (SI).

Purpose of starter batteries
Theoretical foundations for the conversion of chemical energy into electrical energy
Battery discharge
Battery charge
Consumption of the main current-forming reagents
Electromotive force
Internal resistance
Voltage when charging and discharging
Battery capacity
Energy and battery power
Battery self-discharge

Purpose of starter batteries

The main function of the battery is a reliable engine start. Another function is an energy buffer when the engine is running. After all, along with traditional types of consumers, a lot of additional service devices have appeared that improve driver comfort and traffic safety. The battery compensates for the lack of energy when driving in an urban cycle with frequent and long stops, when the generator cannot always provide the power output necessary to fully supply all consumers included. The third working function is power supply when the engine is off. However, prolonged use of electrical appliances while stationary with the engine off (or the engine idling) leads to a deep discharge of the battery and a sharp decrease in its starting performance.

The battery is also designed for emergency power supply. In the event of a failure of the generator, rectifier, voltage regulator, or if the generator belt breaks, it must ensure the operation of all consumers necessary for safe movement to the nearest service station.

So, starter batteries must meet the following basic requirements:

Provide the discharge current necessary for the operation of the starter, that is, have a low internal resistance for minimal internal voltage losses inside the battery;

Provide the required number of attempts to start the engine with a set duration, that is, have the necessary energy reserve of the starter discharge;

Have a sufficiently large power and energy with the smallest possible size and weight;

Have a reserve of energy to power consumers when the engine is not running or in an emergency (reserve capacity);

Maintain the voltage necessary for the operation of the starter when the temperature drops within the specified limits (cold scroll current);

Maintain for a long time performance at elevated (up to 70 "C) ambient temperature;

Receive a charge to restore the capacity used up to start the engine and power other consumers from the generator with the engine running (charge acceptance);

Do not require special user training, maintenance during operation;

Have high mechanical strength corresponding to the operating conditions;

Maintain the specified performance characteristics for a long time during operation (service life);

Possess a slight self-discharge;

Have a low cost.

Theoretical foundations for the conversion of chemical energy into electrical energy

A chemical current source is a device in which, due to the occurrence of spatially separated redox chemical reactions, their free energy is converted into electrical energy. According to the nature of the work, these sources are divided into two groups:

Primary chemical current sources or galvanic cells;

Secondary sources or electric accumulators.

Primary sources allow only a single use, since the substances formed during their discharge cannot be converted into the original active materials. A completely discharged galvanic cell, as a rule, is unsuitable for further work - it is an irreversible source of energy.

Secondary chemical current sources are reversible sources of energy - after an arbitrarily deep discharge, their performance can be fully restored by charging. To do this, it is enough to pass an electric current through the secondary source in the opposite direction to that in which it flowed during the discharge. During the charging process, the substances formed during the discharge will turn into the original active materials. This is how the free energy of a chemical current source is repeatedly converted into electrical energy (battery discharge) and the reverse conversion of electrical energy into free energy of a chemical current source (battery charge).

The passage of current through electrochemical systems is associated with the chemical reactions (transformations) occurring in this case. Therefore, between the amount of a substance that entered into an electrochemical reaction and underwent transformations, and the amount of electricity spent or released in this case, there is a relationship that was established by Michael Faraday.

According to Faraday's first law, the mass of the substance that entered into the electrode reaction or resulting from its occurrence is proportional to the amount of electricity that has passed through the system.

According to Faraday's second law, with an equal amount of electricity passing through the system, the masses of the reacted substances are related to each other as their chemical equivalents.

In practice, a smaller amount of a substance undergoes an electrochemical change than according to Faraday's laws - when current passes, in addition to the main electrochemical reactions, parallel or secondary (side) reactions that change the mass of products also occur. To take into account the influence of such reactions, the concept of current output is introduced.

The current output is that part of the amount of electricity that has passed through the system, which accounts for the main electrochemical reaction under consideration.

Battery discharge

The active substances of a charged lead battery that take part in the current-generating process are:

On the positive electrode - lead dioxide (dark brown);

On the negative electrode - spongy lead (gray);

The electrolyte is an aqueous solution of sulfuric acid.

Some acid molecules in an aqueous solution are always dissociated into positively charged hydrogen ions and negatively charged sulfate ions.

Lead, which is the active mass of the negative electrode, partially dissolves in the electrolyte and oxidizes in solution to form positive ions. The excess electrons released at the same time impart a negative charge to the electrode and begin to move along the closed section of the external circuit to the positive electrode.

Positively charged lead ions react with negatively charged sulfate ions to form lead sulfate, which has little solubility and is therefore deposited on the surface of the negative electrode. In the process of discharging the battery, the active mass of the negative electrode is converted from spongy lead to lead sulfate with a change in gray color to light gray.

The lead dioxide of the positive electrode dissolves in the electrolyte in a much smaller amount than the lead of the negative electrode. When interacting with water, it dissociates (decomposes in solution into charged particles - ions), forming tetravalent lead ions and hydroxyl ions.

The ions give the electrode a positive potential and, by attaching the electrons that came through the external circuit from the negative electrode, are reduced to divalent lead ions

Ions interact with ions to form lead sulphate, which, for the above reason, is also deposited on the surface of the positive electrode, as was the case on the negative. The active mass of the positive electrode, as it is discharged, is converted from lead dioxide to lead sulfate with a change in its color from dark brown to light brown.

As a result of battery discharge, the active materials of both the positive and negative electrodes are converted to lead sulfate. In this case, sulfuric acid is consumed for the formation of lead sulfate and water is formed from the released ions, which leads to a decrease in the density of the electrolyte during discharge.

Battery charge

Both electrodes contain small amounts of lead sulfate and water ions in the electrolyte. Under the influence of the voltage of the DC source, in the circuit of which the rechargeable battery is connected, a directed movement of electrons to the negative terminal of the battery is established in the external circuit.

The divalent lead ions at the negative electrode are neutralized (recovered) by the incoming two electrons, turning the active mass of the negative electrode into spongy metal lead. The remaining free ions form sulfuric acid

At the positive electrode, under the action of a charging current, divalent lead ions give up two electrons, being oxidized into tetravalent ones. The latter, connecting through intermediate reactions with two oxygen ions, form lead dioxide, which is released at the electrode. Ions and, just like at the negative electrode, form sulfuric acid, as a result of which the density of the electrolyte increases during charging.

When the processes of transformation of substances in the active masses of the positive and negative electrodes are over, the density of the electrolyte stops changing, which is a sign of the end of the battery charge. With further continuation of the charge, the so-called secondary process occurs - the electrolytic decomposition of water into oxygen and hydrogen. Standing out from the electrolyte in the form of gas bubbles, they create the effect of its intense boiling, which also serves as a sign of the end of the charging process.

Consumption of the main current-forming reagents

To obtain a capacity of one ampere-hour when the battery is discharged, it is necessary that the following take part in the reaction:

4.463 g lead dioxide

3.886 g spongy lead

3.660 g sulfuric acid

The total theoretical consumption of materials for obtaining 1 Ah (specific consumption of materials) of electricity will be 11.989 g/Ah, and the theoretical specific capacity - 83.41 Ah/kg.

With a nominal battery voltage of 2 V, the theoretical specific consumption of materials per unit of energy is 5.995 g/Wh, and the specific energy of the battery is 166.82 Wh/kg.

However, in practice it is impossible to achieve the full use of active materials that take part in the current-generating process. Approximately half of the surface of the active mass is inaccessible to the electrolyte, since it serves as the basis for constructing a volumetric porous framework that provides the mechanical strength of the material. Therefore, the real utilization rate of the active masses of the positive electrode is 45-55%, and the negative 50-65%. In addition, a 35-38% sulfuric acid solution is used as an electrolyte. Therefore, the value of the actual specific consumption of materials is much higher, and the real values ​​of the specific capacity and specific energy are much lower than the theoretical ones.

Electromotive force

The electromotive force (EMF) of the battery E is the difference in its electrode potentials, measured with an open external circuit.

EMF of a battery consisting of n series-connected batteries.

It is necessary to distinguish between the equilibrium EMF of the battery and the non-equilibrium EMF of the battery during the time from opening the circuit to establishing an equilibrium state (the period of the transition process).

EMF is measured with a high-resistance voltmeter (internal resistance not less than 300 Ohm/V). To do this, a voltmeter is connected to the terminals of the battery or battery. In this case, no charging or discharging current should flow through the accumulator (battery).

The equilibrium EMF of a lead battery, like that of any chemical current source, depends on the chemical and physical properties of the substances involved in the current-generating process, and is completely independent of the size and shape of the electrodes, as well as the amount of active masses and electrolyte. At the same time, in a lead battery, the electrolyte is directly involved in the current-generating process on the battery electrodes and changes its density depending on the degree of charge of the batteries. Therefore, the equilibrium emf, which in turn is a function of density

The change in the EMF of the battery with temperature is very small and can be neglected during operation.

Internal resistance

The resistance provided by the battery to the current flowing inside it (charging or discharging) is commonly called the internal resistance of the battery.

The resistance of the active materials of the positive and negative electrodes, as well as the resistance of the electrolyte, change depending on the state of charge of the battery. In addition, the resistance of the electrolyte is highly dependent on temperature.

Therefore, the ohmic resistance also depends on the state of charge of the battery and the temperature of the electrolyte.

The polarization resistance depends on the strength of the discharge (charging) current and temperature and does not obey Ohm's law.

The internal resistance of a single battery, and even a battery consisting of several series-connected batteries, is insignificant and is only a few thousandths of an ohm in a charged state. However, during the discharge process, it changes significantly.

The electrical conductivity of the active masses decreases for the positive electrode by about 20 times, and for the negative electrode by 10 times. The electrical conductivity of an electrolyte also varies with its density. With an increase in electrolyte density from 1.00 to 1.70 g/cm3, its electrical conductivity first increases to its maximum value, and then decreases again.

As the battery discharges, the density of the electrolyte decreases from 1.28 g/cm3 to 1.09 g/cm3, which leads to a decrease in its electrical conductivity by almost 2.5 times. As a result, the ohmic resistance of the battery increases as it discharges. In the discharged state, the resistance reaches a value that is more than 2 times higher than its value in the charged state.

In addition to the state of charge, temperature has a significant effect on the resistance of batteries. With decreasing temperature, the specific resistance of the electrolyte increases and at a temperature of -40 °C becomes approximately 8 times greater than at +30 °C. The resistance of the separators also sharply increases with decreasing temperature and in the same temperature range increases by almost 4 times. This is the determining factor in increasing the internal resistance of batteries at low temperatures.

Voltage when charging and discharging

The potential difference at the pole terminals of the battery (battery) in the process of charging or discharging in the presence of current in the external circuit is commonly called the voltage of the battery (battery). The presence of the internal resistance of the battery leads to the fact that its voltage during discharge is always less than the EMF, and when charging it is always greater than the EMF.

When the battery is charging, the voltage at its terminals must be greater than its EMF by the amount of internal losses.

At the beginning of the charge, there is a voltage jump by the amount of ohmic losses inside the battery, and then a sharp increase in voltage due to the polarization potential, caused mainly by a rapid increase in the density of the electrolyte in the pores of the active mass. Then there is a slow increase in voltage, due mainly to an increase in the EMF of the battery due to an increase in the density of the electrolyte.

After the main amount of lead sulfate is converted into PbO2 and Pb, the energy costs increasingly cause the decomposition of water (electrolysis). The excess amount of hydrogen and oxygen ions that appear in the electrolyte further increases the potential difference of opposite electrodes. This leads to a rapid increase in the charging voltage, causing an acceleration of the process of water decomposition. The resulting hydrogen and oxygen ions do not interact with active materials. They recombine into neutral molecules and are released from the electrolyte in the form of gas bubbles (oxygen is released at the positive electrode, hydrogen is released at the negative), causing the electrolyte to "boil".

If you continue the charging process, you can see that the increase in electrolyte density and charging voltage practically stops, since almost all of the lead sulfate has already reacted, and all the energy supplied to the battery is now spent only on the side process - the electrolytic decomposition of water. This explains the constancy of the charging voltage, which is one of the signs of the end of the charging process.

After the charge is terminated, that is, the external source is turned off, the voltage at the battery terminals drops sharply to the value of its non-equilibrium EMF, or to the value of ohmic internal losses. Then there is a gradual decrease in the EMF (due to a decrease in the density of the electrolyte in the pores of the active mass), which continues until the electrolyte concentration in the volume of the battery and the pores of the active mass is completely equalized, which corresponds to the establishment of an equilibrium EMF.

When the battery is discharged, the voltage at its terminals is less than the EMF by the value of the internal voltage drop.

At the beginning of the discharge, the battery voltage drops sharply by the amount of ohmic losses and polarization due to a decrease in the electrolyte concentration in the pores of the active mass, that is, concentration polarization. Further, during the steady-state (stationary) discharge process, the density of the electrolyte decreases in the volume of the battery, causing a gradual decrease in the discharge voltage. At the same time, there is a change in the ratio of the content of lead sulfate in the active mass, which also causes an increase in ohmic losses. In this case, lead sulfate particles (having approximately three times the volume in comparison with the particles of lead and its dioxide from which they were formed) close the pores of the active mass, which prevents the electrolyte from passing into the depth of the electrodes.

This causes an increase in the concentration polarization, which leads to a more rapid decrease in the discharge voltage.

When the discharge stops, the voltage at the battery terminals quickly increases by the amount of ohmic losses, reaching the value of non-equilibrium EMF. A further change in the EMF due to the alignment of the electrolyte concentration in the pores of the active masses and in the volume of the battery leads to a gradual establishment of the value of the equilibrium EMF.

The voltage of the battery during its discharge is determined mainly by the temperature of the electrolyte and the strength of the discharge current. As mentioned above, the resistance of a lead accumulator (battery) is insignificant and in a charged state is only a few milliohms. However, at starter discharge currents, the strength of which is 4-7 times higher than the nominal capacitance, the internal voltage drop has a significant effect on the discharge voltage. The increase in ohmic losses with decreasing temperature is associated with an increase in the resistance of the electrolyte. In addition, the viscosity of the electrolyte increases sharply, which makes it difficult for it to diffuse into the pores of the active mass and increases the concentration polarization (that is, it increases the voltage loss inside the battery due to a decrease in the electrolyte concentration in the pores of the electrodes).

At a current of more than 60 A, the dependence of the discharge voltage on the current strength is almost linear at all temperatures.

The average value of the battery voltage during charging and discharging is determined as the arithmetic mean of the voltage values ​​measured at equal time intervals.

Battery capacity

Battery capacity is the amount of electricity received from the battery when it is discharged to the set final voltage. In practical calculations, the battery capacity is usually expressed in ampere-hours (Ah). Discharge capacity can be calculated by multiplying the discharge current by the duration of the discharge.

The discharge capacity for which the battery is designed and which is specified by the manufacturer is called the nominal capacity.

In addition to it, an important indicator is also the capacity reported to the battery when charging.

Discharge capacity depends on a number of design and technological parameters of the battery, as well as its operating conditions. The most significant design parameters are the amount of active mass and electrolyte, the thickness and geometric dimensions of the battery electrodes. The main technological parameters that affect the battery capacity are the formulation of active materials and their porosity. Operating parameters - the temperature of the electrolyte and the strength of the discharge current - also have a significant impact on the discharge capacity. A generalized indicator that characterizes the efficiency of the battery is the utilization rate of active materials.

To obtain a capacity of 1 Ah, as mentioned above, theoretically, 4.463 g of lead dioxide, 3.886 g of spongy lead and 3.66 g of sulfuric acid are needed. The theoretical specific consumption of the active masses of the electrodes is 8.32 g/Ah. In real batteries, the specific consumption of active materials in a 20-hour discharge mode and an electrolyte temperature of 25 °C is from 15.0 to 18.5 g/Ah, which corresponds to an active mass utilization rate of 45–55%. Therefore, the practical consumption of the active mass exceeds the theoretical values ​​by 2 or more times.

The following main factors influence the degree of use of the active mass, and, consequently, the value of the discharge capacity.

Porosity of the active mass. With an increase in porosity, the conditions for electrolyte diffusion into the depth of the active mass of the electrode improve and the true surface on which the current-forming reaction proceeds increases. With increasing porosity, the discharge capacity increases. The value of porosity depends on the particle size of the lead powder and the recipe for the preparation of active masses, as well as on the additives used. Moreover, an increase in porosity leads to a decrease in durability due to the acceleration of the process of destruction of highly porous active masses. Therefore, the porosity value is chosen by manufacturers, taking into account not only high capacitive characteristics, but also ensuring the necessary durability of the battery in operation. Currently, porosity is considered to be optimal in the range of 46-60%, depending on the purpose of the battery.

The thickness of the electrodes. With a decrease in thickness, the uneven loading of the outer and inner layers of the active mass of the electrode decreases, which contributes to an increase in the discharge capacity. For thicker electrodes, the inner layers of the active mass are used very little, especially when discharging with high currents. Therefore, with an increase in the discharge current, the differences in the capacity of batteries with electrodes of different thicknesses sharply decrease.

Porosity and rationality of the separator material design. With an increase in the porosity of the separator and the height of its ribs, the supply of electrolyte in the interelectrode gap increases and the conditions for its diffusion improve.

electrolyte density. Affects the capacity of the battery and its service life. With an increase in the density of the electrolyte, the capacitance of the positive electrodes increases, and the capacitance of the negative ones, especially at negative temperatures, decreases due to the acceleration of the passivation of the electrode surface. Increased density also has a negative effect on battery life due to the acceleration of corrosion processes at the positive electrode. Therefore, the optimal density of the electrolyte is set based on the totality of requirements and conditions in which the battery is operated. So, for example, for starter batteries operating in a temperate climate, an electrolyte working density of 1.26-1.28 g/cm3 is recommended, and for areas with a hot (tropical) climate, 1.22-1.24 g/cm3.

The strength of the discharge current with which the battery must be continuously discharged for a given time (characterizes the discharge mode). Discharge modes are conditionally divided into long and short. In long-term modes, the discharge occurs with small currents for several hours. For example, 5-, 10-, and 20-hour discharges. With short or starter discharges, the current strength is several times greater than the nominal capacity of the battery, and the discharge lasts several minutes or seconds. With an increase in the discharge current, the discharge rate of the surface layers of the active mass increases to a greater extent than the deep ones. As a result, the growth of lead sulfate in the mouths of the pores occurs faster than in the depths, and the pore is clogged with sulfate before its inner surface has time to react. Due to the cessation of electrolyte diffusion into the pore, the reaction in it stops. Thus, the greater the discharge current, the lower the battery capacity, and hence the active mass utilization factor.

To assess the starting qualities of batteries, their capacity is also characterized by the number of intermittent starter discharges (for example, a duration of 10-15 s with breaks between them of 60 s). The capacity that the battery gives out during intermittent discharges exceeds the capacity during continuous discharge with the same current, especially in the starter discharge mode.

Currently, in the international practice of assessing the capacitive characteristics of starter batteries, the concept of "reserve" capacity is used. It characterizes the battery discharge time (in minutes) at a discharge current of 25 A, regardless of the nominal battery capacity. At the discretion of the manufacturer, it is allowed to set the value of the nominal capacity at a 20-hour discharge mode in ampere-hours or by reserve capacity in minutes.

electrolyte temperature. With its decrease, the discharge capacity of the batteries decreases. The reason for this is an increase in the viscosity of the electrolyte and its electrical resistance, which slows down the rate of diffusion of the electrolyte into the pores of the active mass. In addition, with decreasing temperature, the processes of passivation of the negative electrode are accelerated.

The temperature coefficient of capacitance a shows the change in capacitance in percent for a change in temperature of 1 °C.

During tests, the discharge capacity obtained in a long-term discharge mode is compared with the nominal capacity value determined at an electrolyte temperature of +25 °C.

The temperature of the electrolyte when determining the capacity in a long-term discharge mode in accordance with the requirements of the standards should be in the range from +18 °C to +27 °C.

The parameters of the starter discharge are estimated by the duration of the discharge in minutes and the voltage at the beginning of the discharge. These parameters are determined on the first cycle at +25°C (test for dry batteries) and on subsequent cycles at temperatures of -18°C or -30°C.

The degree of charge. With an increase in the degree of charge, other things being equal, the capacity increases and reaches its maximum value when the batteries are fully charged. This is due to the fact that with an incomplete charge, the amount of active materials on both electrodes, as well as the density of the electrolyte, do not reach their maximum values.

Energy and battery power

The battery energy W is expressed in Watt-hours and is determined by the product of its discharge (charging) capacity by the average discharge (charging) voltage.

Since the battery capacity and its discharge voltage change with a change in temperature and discharge mode, with a decrease in temperature and an increase in the discharge current, the energy of the battery decreases even more significantly than its capacity.

When comparing chemical current sources with each other, differing in capacity, design, and even in an electrochemical system, as well as in determining the directions for their improvement, they use the specific energy indicator, i.e. the energy per unit mass of the battery or its volume. For modern lead starter maintenance-free batteries, the specific energy for a 20-hour discharge is 40-47 Wh/kg.

The amount of energy given off by a battery per unit of time is called its power. It can be defined as the product of the magnitude of the discharge current and the average discharge voltage.

Battery self-discharge

Self-discharge is a decrease in the capacity of batteries with an open external circuit, that is, with inactivity. This phenomenon is caused by redox processes that spontaneously occur on both the negative and positive electrodes.

The negative electrode is especially susceptible to self-discharge due to the spontaneous dissolution of lead (negative active mass) in a solution of sulfuric acid.

The self-discharge of the negative electrode is accompanied by the evolution of hydrogen gas. The rate of spontaneous dissolution of lead increases significantly with increasing electrolyte concentration. An increase in the density of the electrolyte from 1.27 to 1.32 g/cm3 leads to an increase in the self-discharge rate of the negative electrode by 40%.

The presence of impurities of various metals on the surface of the negative electrode has a very significant effect (catalytic) on the increase in the rate of self-dissolution of lead (due to a decrease in the overvoltage of hydrogen evolution). Almost all metals found as impurities in battery raw materials, electrolyte and separators, or introduced in the form of special additives, contribute to an increase in self-discharge. Getting on the surface of the negative electrode, they facilitate the conditions for hydrogen evolution.

Some impurities (salts of metals with variable valence) act as charge carriers from one electrode to another. In this case, metal ions are reduced at the negative electrode and oxidized at the positive one (this self-discharge mechanism is attributed to iron ions).

The self-discharge of the positive active material is due to the progress of the reaction.

2PbO2 + 2H2SO4 -> PbSCU + 2H2O + O2 T.

The rate of this reaction also increases with increasing electrolyte concentration.

Since the reaction proceeds with the release of oxygen, its rate is largely determined by the oxygen overvoltage. Therefore, additives that reduce the potential for oxygen evolution (for example, antimony, cobalt, silver) will increase the rate of the reaction of self-dissolution of lead dioxide. The self-discharge rate of the positive active material is several times lower than the self-discharge rate of the negative active material.

Another reason for self-discharge of the positive electrode is the potential difference between the current collector material and the active mass of this electrode. The galvanic microelement arising as a result of this potential difference converts the lead of the current collector and the lead dioxide of the positive active mass into lead sulfate when the current flows.

Self-discharge can also occur when the outside of the battery is dirty or flooded with electrolyte, water or other liquids that allow discharge through the electrically conductive film located between the battery terminals or its jumpers. This type of self-discharge does not differ from the usual discharge by very small currents with a closed external circuit and can be easily eliminated. To do this, keep the surface of the batteries clean.

The self-discharge of batteries is largely dependent on the temperature of the electrolyte. With decreasing temperature, self-discharge decreases. At temperatures below 0 ° C for new batteries, it practically stops. Therefore, storage of batteries is recommended in a charged state at low temperatures (up to -30 °C).

During operation, self-discharge does not remain constant and sharply increases towards the end of the service life.

Reducing self-discharge is possible by increasing the overvoltage of oxygen and hydrogen emissions on the battery electrodes.

To do this, it is necessary, firstly, to use the purest possible materials for the production of batteries, to reduce the quantitative content of alloying elements in battery alloys, to use only

pure sulfuric acid and distilled (or close to it in purity with other purification methods) water for the preparation of all electrolytes, both during production and during operation. For example, due to the reduction of the antimony content in the current lead alloy from 5% to 2% and the use of distilled water for all process electrolytes, the average daily self-discharge is reduced by 4 times. Replacing antimony with calcium makes it possible to further reduce the self-discharge rate.

The addition of organic substances - self-discharge inhibitors - can also contribute to a decrease in self-discharge.

The use of a common cover and hidden interconnects significantly reduces the self-discharge rate from leakage currents, since the probability of galvanic coupling between far-spaced pole terminals is significantly reduced.

Self-discharge is sometimes referred to as a rapid loss of capacity due to a short circuit inside the battery. This phenomenon is explained by a direct discharge through conductive bridges formed between opposite electrodes.

The use of envelope separators in maintenance-free batteries

eliminates the possibility of short circuits between opposite electrodes during operation. However, this probability remains due to possible failures in the operation of equipment during mass production. Typically, such a defect is detected in the first months of operation and the battery must be replaced under warranty.

Usually, the degree of self-discharge is expressed as a percentage of capacity loss over a specified period of time.

Self-discharge is also characterized by the current standards by the voltage of the starter discharge at -18 °C after the test: inactivity for 21 days at a temperature of +40 °C.

Battery voltage, along with the capacity and density of the electrolyte, allows you to draw a conclusion about the condition of the battery. By the voltage of a car battery, you can judge the degree of its charge. If you want to be aware of the status of your battery and take proper care of it, then you definitely need to learn how to control the voltage. What's more, it's quite easy. And we will try to explain in an accessible way how this is done and what tools are needed.

First you need to decide on the concepts of voltage and electromotive force (EMF) of a car battery. EMF ensures the flow of current through the circuit and provides a potential difference at the terminals of the power supply. In our case, this is a car battery. The battery voltage is determined by the potential difference.

EMF is a value that is equal to the work expended on moving a positive charge between the terminals of a power source. The values ​​of voltage and electromotive forces are inextricably linked. If there is no electromotive force in the battery, then there will be no voltage at its terminals. It should also be said that voltage and EMF exist without the passage of current in the circuit. In the open state, there is no current in the circuit, but an electromotive force is still excited in the battery and there is voltage at the terminals.

Both quantities, emf and car battery voltage, are measured in volts. It is also worth adding that the electromotive force in a car battery arises due to the flow of electrochemical reactions inside it. The dependence of EMF and battery voltage can be expressed by the following formula:

E = U + I*R 0 where

E is the electromotive force;

U is the voltage at the battery terminals;

I is the current in the circuit;

R 0 - internal resistance of the battery.

As can be understood from this formula, the EMF is greater than the battery voltage by the amount of voltage drop inside it. In order not to fill your head with unnecessary information, let's put it simply. The electromotive force of the battery is the voltage at the battery terminals without taking into account the leakage current and external load. That is, if you remove the battery from the car and measure the voltage, then in such an open circuit it will be equal to the EMF.

Voltage measurements are made with instruments such as a voltmeter or multimeter. In a battery, the EMF value depends on the density and temperature of the electrolyte. With an increase in the density of the electrolyte, the voltage and EMF also increase. For example, at an electrolyte density of 1.27 g / cm 3 and a temperature of 18 C, the battery bank voltage is 2.12 volts. And for a battery consisting of six cells, the voltage value will be 12.7 volts. This is the normal voltage of a car battery that is charged and not under load.

Normal car battery voltage

The voltage on the car battery should be 12.6-12.9 volts if it is fully charged. Measuring the battery voltage allows you to quickly assess the degree of charge. But the real condition and deterioration of the battery by voltage cannot be known. To get reliable data on the condition of the battery, you need to check its real and carry out a test under load, which will be discussed below. We advise you to read the material on how.

However, with the help of voltage, you can always find out the state of charge of the battery. Below is a table of the state of charge of the battery, which shows the voltage, density and freezing point of the electrolyte, depending on the battery charge.

			The degree of battery charge,%
Electrolyte density, g/cm. cube (+15 gr. Celsius)	Voltage, V (in the absence of load)	Voltage, V (with a load of 100 A)	The degree of battery charge,%	Freezing point of electrolyte, gr. Celsius
1,11	11,7	8,4	0	-7
1,12	11,76	8,54	6	-8
1,13	11,82	8,68	12,56	-9
1,14	11,88	8,84	19	-11
1,15	11,94	9	25	-13
1,16	12	9,14	31	-14
1,17	12,06	9,3	37,5	-16
1,18	12,12	9,46	44	-18
1,19	12,18	9,6	50	-24
1,2	12,24	9,74	56	-27
1,21	12,3	9,9	62,5	-32
1,22	12,36	10,06	69	-37
1,23	12,42	10,2	75	-42
1,24	12,48	10,34	81	-46
1,25	12,54	10,5	87,5	-50
1,26	12,6	10,66	94	-55
1,27	12,66	10,8	100	-60

We advise you to periodically check the voltage and charge the battery as needed. If the voltage of the car battery drops below 12 volts, it must be recharged from the mains charger. Its operation in this state is highly discouraged.

Battery operation in a discharged state leads to an increase in sulphation of the plates and, as a result, a drop in capacity. In addition, this can lead to a deep discharge, which is similar to death for calcium batteries. For them, 2-3 deep discharges is a direct path to a landfill.

Well, now about what kind of tool a motorist needs to control the voltage and condition of the battery.

Car Battery Voltage Monitoring Tools

Now that you know what normal car battery voltage is, let's talk about measuring it. To control the voltage, you need a multimeter (also called a tester) or a regular voltmeter.

To measure voltage with a multimeter, you need to switch it to voltage measurement mode, and then attach the probes to the battery terminals. The battery must be removed from the car or the terminals removed from it. That is, measurements are taken on an open circuit. The red probe goes to the positive terminal, the black one to the negative terminal. The display will show the voltage value. If you mix up the probes, nothing bad will happen. Just a multimeter will show a negative voltage value. Read more about the article at the link provided.

There is also such a device as a load fork. They can also measure voltage. To do this, the load plug has a built-in voltmeter. But much more interesting for us is that the load plug allows you to measure the voltage of the battery in a closed circuit with resistance. Based on these readings, you can judge the state of the battery. In fact, the load fork creates an imitation of starting a car engine.

To measure the voltage under load, connect the terminals of the load plug to the battery terminals and turn on the load for 5 seconds. At the fifth second, look at the readings of the built-in voltmeter. If the voltage dipped below 9 volts, then the battery has already failed and should be replaced. Of course, provided the battery is fully charged and in an open circuit it produces a voltage of 12.6-12.9 volts. On a working battery, when a load is applied, the voltage will first drop somewhere up to 10-10.5 volts, and then begin to grow slightly.

What should be remembered?

In conclusion, here are some tips that will save you from mistakes when operating the battery:

• periodically measure the battery voltage and regularly (once every 3 months) recharge it from a mains charger;
• keep the alternator, wiring and voltage regulator of the car in good condition to properly charge the battery when traveling. The value of the leakage current must be checked regularly. and its measurement are described in the article by reference;
• check the density of the electrolyte after charging and refer to the table above;
• keep the battery clean. This will reduce the leakage current.

Attention! Never short-circuit the terminals of a car battery. The consequences will be sad.

That's all I wanted to say about the voltage of the car battery. If you have additions, corrections and questions, write them in the comments. Happy battery life!

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