How to determine the state of charge of a car battery

Car battery charging voltage

A lack of charge in a car battery may be an indicator of problems with the generator or lack of timely recharging. When this indicator drops to critically low values, there is a risk that the car will “freeze” and the owner will not be able to start it. Therefore, a car enthusiast should be able to determine the battery charge by voltage; a table of indicators can help him with this.

Battery charging voltage with car charger

If the car owner drives mainly long distances, the battery manages to replenish most of the charge from the generator during the run. The degree of charge is assessed by the indicator on the terminals: the higher the indicator, the more electrolyte.

The battery capacity is replenished using a charger operating on the conversion principle. Batteries can be classified according to a number of criteria. For example, they can be maintained or unattended and use different chemical agents (gel, lithium, etc.).

You can evaluate the degree of charge using a multimeter (by setting the voltage measurement mode) or a voltmeter. The ends of the wires are applied to the terminals. Since in this case only the number is important, it is not necessary to monitor the polarity. If the user confuses the red and black wires, the device will simply show a negative value, but in modulus it will correspond to the desired one.

The optimal charge level is indicated by indicators in the range from 12 to 16 Volts. When the number drops below 12, you should not use the battery - lead sulfate will settle on its plates, and this leads to a decrease in capacity and deterioration in performance. A deep discharge of the battery (a drop below 10.8) can lead to failure.

Voltage at battery terminals when charging

The battery is powered from the charger using a program with a constant voltage or current. When it is charging, you need to measure the data on the clamps. Measurements are performed only with the engine running. The optimum is 13-14 V. If it is high, the battery needs to be recharged; if it is low, there is a problem with the generator or the battery is depleting its resource.

If the number is in the range of 12-14 V, there is no need to worry.

If it is lower, you need to check:

• transparency and electrolyte level;
• presence of deposits on the plates;
• the ability to recharge the battery to normal condition.

Charging a battery with constant resistance

If you set the resistance to a constant, the voltage or current will take variable values. But the resistance inside a car battery is always a variable value, which is influenced by a number of factors: electrolyte saturation, state of charge, temperature. The total value is the sum of two: polarization resistance (not a constant value) and ohmic (constant for a battery).

Since resistance is an unstable quantity depending on the state of the battery, voltage, current, or a combination of both can be taken as a constant. The ballast resistance smoothes the charging flow.

What voltage should I set when charging the battery?

The charging parameter is always set to exceed the battery charge level. The more pronounced the difference, the sooner the battery will charge to the desired level.

This difference also affects the completeness of charging, and the ratio looks like this:

• to charge a 12 V battery, you will need to set the level to 16-16.5 V (then the battery will be fully charged);
• when using a value of 15 V, the battery can be filled to 85-88%;
• a parameter of 14.5 V gives 77-80% charge.

When the indicator at the battery terminals reaches 14.5 V, the device will notify you with a signal that charging is complete. Since this level does not provoke the release of gases when recharging the battery and after its completion, after some time of operation of the machine, the generator will limit the indicator to this figure.

Maximum battery charging voltage

The highest value used on the charger when recharging the battery is 16.5 V. Setting it will allow the battery to quickly reach its maximum capacity. However, it is not advisable to use such a voltage for all batteries. Calcium maintenance-free products are designed for it, capable of withstanding intense power supply with the accompanying boiling of the electrolyte.

Battery voltage at the end of charging

When the charging process is completed, after some time the electrolyte begins to dissociate, fill the pores of the plates and adapt to the temperature of the environment, which is why the charge level changes slightly. In hot weather it rises; when the air temperature is below zero, it falls.

To find out the final voltage, you need to measure it at the terminals with the motor turned on. If the indicator on a running car after charging begins to drop sharply, you need to diagnose the condition of the generator or replace the battery.

Dependence of battery charging on voltage

To quickly assess the battery charge level and, if necessary, use the charger, the car owner must be able to determine by the voltage at the terminals how many percent the device is charged . The indicator correspondence table will help with this.

Car battery charging voltage

Before connecting the charger, the battery charge is checked by voltage; the table helps to find out its condition. Depending on the voltmeter readings, select the capacity restoration mode.

Battery charging voltage with car charger

The battery is recharged while the engine is running, when it releases energy, by a car generator. If its operation is unstable, then the capacity is not restored. When driving long distances, the battery is charged, there is enough energy to start the engine, but the capacity is not 100% filled. This is provided by design so that the battery does not overcharge.

Check the condition of the battery and at the same time the car charger with a voltmeter in voltage measurement mode. The red probe touches the positive terminal, the black probe touches the negative terminal. If you connect it the other way around, the device will simply show a negative value. The on-board voltmeter is not directly connected to the battery, so there are errors in the readings.

First, they measure with an open circuit: remove the battery or disconnect the terminals. Normally, the readings should be from 12.6 to 12.9V. If they are smaller, there is a problem with the battery or the generator does not provide it with current to restore capacity.

A more accurate picture of the degree of charge is given by measurements with the internal combustion engine running without lighting:

• from 13.0 to 13.4V – a slight drop in capacity, recharging is required;
• from 13.5 to 14.0V – the condition of the battery and charging equipment is normal;
• above 14V - the battery is discharged (if in the winter after some time the indicators return to normal, the system is in order).

Charging is carried out using an external device.

Voltage at battery terminals when charging

Charge with constant amperes or volts on the charger. To know the charge of the battery, monitor the voltage at its contacts. It grows, the charging current drops. If measurements show that it does not increase over 2 hours, and the amperage is stable, then the battery has filled its capacity to almost 100%.

The voltage rises to the same as that of the memory. The recommended value is from 14.4 to 14.5V. When the voltage on the device and the battery terminals is equal, this means that 90-95% of the charge has been achieved. The most modern maintenance-free batteries require 16.1-16.3V. The same indicator should be on the terminals.

Charging a battery with constant resistance

Charging with a stable current is the main universal method of restoring capacity. Amps remain unchanged. You can charge in another way by applying voltage without changing. The process is faster, but the amp readings drop as the capacity increases.

According to Ohm's law, if you maintain a constant resistance, then the voltage will change during the charging process. But the battery has an internal variable resistance. It changes depending on charge, load and other factors. If the resistance is variable, then the volts or amperes will be stable.

What voltage should I set when charging the battery?

To start charging, the charger requires more voltage than is available on the battery. The more significant the difference between them, the faster the capacity is gained. There are rise limits beyond which the electrolyte begins to boil.

If you set the optimal parameter, then the most complete charge occurs, there is no gas evolution. On a car, the voltage is limited by a relay, so if the system is working properly, the battery is not in danger of overcharging and boiling of the electrolyte. If external storage is used, then the indicator is set manually.

Maximum battery charging voltage

It is affected by the type of battery. The voltage determines how quickly and how completely the capacity will be restored.

All batteries, except calcium ones, are charged primarily with a stable current or voltage. With a constant amperage, it is set to 10% of the battery capacity. Charge until the voltmeter shows 14.3-14.4V. The amperes are then halved and charging continues. When the voltage rises to 15V, the amperage is again reduced by 2 times. Charge until the volts and amperes stabilize.

Using the constant voltage method, the charger is set to the maximum value - 14.4V and wait. When the readings on the charger and terminals are equal, we can assume that the battery is charged.

In luxury cars, the on-board system operates on 16V, the battery is recharged with increased current. Acid devices are unable to withstand it, so maintenance-free Ca/Ca are used. They have a closed system, no gas emission, and can withstand harsh operating conditions. However, deep discharge and incorrect operation of the on-board network system are not allowed.

The use of calcium batteries is justified in vehicles where good equipment is installed to monitor the on-board electrical system. Such batteries need to be charged up to 16V using a special mode. A special programmable memory is used, capable of delivering 16.1-16.5V. With this voltage, the calcium battery is charged to 100%. If the device produces no more than 14.8V, then the capacity will be replenished by 50%. When limited to 15.5V Ca/Ca, the battery will be charged to 75%.

Battery voltage at the end of charging

The end of the charge is indicated by 14.4V on the tester. On factory devices this is indicated by a green indicator light. If charging is incomplete, the voltage will begin to drop after a few hours. If it changes downward while the car is running, then we can judge that the battery or generator is faulty.

Deviations from the correct voltage at the end of charging are dangerous. If the voltage is insufficient, the battery will not charge and will sulfate. And if gases escape during charging, the temperature of the electrolyte rises. The consequences can be dangerous: the resource decreases more.

Dependence of battery charging on voltage

When charging with a stable voltage, there is a direct dependence of the battery capacity on the voltage supplied from the charger:

Each battery is charged in the mode provided for by the design. The lowest voltage is required for serviceable acid and gel batteries. The highest is for calcium. Charging stops when the nominal value is reached.

Battery charge level table

The battery capacity is measured with a tester by disconnecting the charging from the network. To obtain more accurate data, readings are taken under a load of 100A. Voltage also characterizes the density of the electrolyte and its freezing point.

Rechargeable batteries

Information site about energy storage devices

Car battery charging voltage

A car battery consists of 6 cells connected in series. Each bank has a full charge of 2.10-2.15 V, so the total voltage is summed up and is 12.6 - 12.8 V. What is the voltage of the battery after the charger is turned off? When installing the battery in a car, the voltage after charging should be 12.4 V. This is normal. The car's starter battery is discharged during engine startup and, while driving, it recovers energy from the car's generator. If the battery voltage drops to 12 V, the device requires charging from the network. A large loss of charge in banks is characterized as a deep discharge that destroys the battery.

Battery charging voltage with car charger

A car operated with the advantage of long runs has time to be fully charged from the generator for the next start. But its charge will not be full. The state of charge of the battery can be determined by the voltage at the terminals. The lower the value, the weaker the electrolyte concentration in the jars.

You can check the battery charge using a multimeter. You should set the “alternating current” calibration and measure the indicator at the terminals. You can determine the charge level by the density of the electrolyte.

The degree of charge of a car battery is determined by voltage, as in the table.

To increase the battery capacity, you need to charge it with a special charger. This is a voltage converter, rectifier. Batteries are serviced, maintenance-free, gel, AGM, lithium. Their charging voltage and current differ in voltage, time, and cycle duration. There are universal chargers designed to switch modes for different battery models and regulate parameters.

Voltage at battery terminals when charging

To charge the battery from a charger, select a mode with constant current or voltage. Both are equally effective, but apply to different batteries. During charging and operating the battery, it is necessary to measure the voltage at the terminals of the acid battery.

To charge a 12 V battery, you will need to set the constant voltage mode to 16 -16.5 V. Using a current of 14.4 V, you can charge the battery by 75-85%. At a constant voltage, the charging current is variable and is limited only by the charger.

What charging voltage should I set? They proceed from the achievement of a critical voltage, accompanied by “boiling” - the release of gas from the car battery cans. A battery is considered to be normally charged, with a voltage at the terminals from 12.6 to 14.5 V. Readings should be taken with the device, without relying on the on-board computer. The measurements with the engine running and with the battery disconnected are different.

The permissible charging voltage at the battery terminals when the engine is running varies from 13.5 -14 V. The indicator shows the battery is undercharged if the voltage is higher. You need to repeat the measurement after 2 minutes, the battery may have been discharged during startup. If the charging voltage is low, the battery is losing its life or the problems are coming from the car alternator. Measurements must be taken by turning off the on-board systems.

By measuring the battery charging voltage with the car not running, it is impossible to identify problems with the generator, but the degree of battery charge is well determined. A voltage of 12.5 - 14 V indicates no problems. If the indicator is low, you need to check:

• electrolyte condition - the substance should be transparent, the level should be normal;
• a lot depends on the battery charge level;
• determining the possibility of recharging to the optimal voltage.

Testing will reveal problems with the battery and its performance.

Charging a battery with constant resistance

Is it possible to charge a battery with a constant resistance? From the formula I =U*R, it is clear that if you set the resistance to a constant value, then the current or voltage will become variable. But inside the battery, resistance is a variable value that affects energy absorption. The total resistance consists of the polarization resistance, which changes, and the ohmic resistance, which remains stable under the same conditions and for a particular battery.

The resistance is affected by temperature, degree of discharge, and electrolyte concentration, which are taken into account in the characteristics of the battery discharge curves. But if in the formula resistance is a variable value over time and the state of the car battery, then current, voltage, or a combination of current and voltage can be constant during charging. To smooth out the charging current, a resistor is used - ballast resistance.

What voltage should I set when charging the battery?

Voltage is a potential difference, and the current will flow in the direction where this value is smaller. Therefore, the charger voltage is always selected higher than the charging level of the car battery. The greater the voltage difference, the faster and more fully the car battery will gain capacity after charging.

During charging at a constant voltage, the limit of the parameter set on the charger is lower than the characteristic at which the release of gases from the battery being serviced begins. What potential difference is needed to charge a car battery? The maximum voltage used when charging the battery is 16.5 V. Which parameter should be depends on the type of battery. The time and completeness of battery charging depends on the voltage. The ratio of charge voltage and capacity recovery for a 12 V battery in 24 hours is as follows:

• With a voltage of 14.4 V you can charge the battery by 75-80%;
• Using a voltage of 15 V, the charge level is 85 - 90%;
• With a voltage of 16 V, the battery is charged by 95 - 97%;
• With a maximum voltage of 16.3 -16.5 V, the batteries are fully charged.

When the battery voltage reaches 14.4 - 14.5, the charging end signal lights up on the charger.

It has been established that it is this voltage of the car battery that does not create gas emissions after and during charging. Therefore, during actual vehicle operation, the generator, through a voltage regulator, limits the maximum voltage level to this value. In summer this figure is close to 100% capacity, in winter it corresponds to 13.9-14.3 V, with the engine running, which corresponds to 70-75% capacity.

Maximum battery charging voltage

We know that modern high-class cars have an on-board system that runs on 16 V. What batteries are used in these batteries? To avoid gas emissions, the system must be closed.

This means that maintenance-free Ca/Ca batteries can withstand harsh operating conditions. They use a special charging mode. Using calcium instead of antimony allows the battery to be charged at higher voltage, which causes the electrolyte to boil. A maintenance-free battery does not tolerate sudden changes in voltage in the on-board network. It is designed for vehicles with a good electronic voltage control system. Hybrid batteries made from low-antimony and calcium plates are more tolerant of operating conditions.

Battery voltage at the end of charging

After the battery is fully charged, the charge will change slightly. The electrolyte dissociates and the pores of the current-carrying plates are filled. A car battery installed in the engine compartment takes in the ambient temperature, and the capacity will increase in the heat or decrease at sub-zero temperatures. Therefore, after charging, you can find out exactly what the voltage of the car’s battery is by installing it in place. Even while in the workshop, the voltage at the terminals changes. This is especially noticeable if the cycle is not completed and the charging current has not dropped to 200 mA. In this case, charge redistribution occurs, and additional energy replenishment of the device is possible.

But if, after charging the battery, the voltage drops while the car is running, this is a reason to inspect the generator or replace the battery.

Dependence of battery charging on voltage

Each type of battery is charged based on the characteristics of the types of designs used. Serviced, gel and lithium batteries have the lowest charging voltage. Causes: boiling over, destruction of the composition, fire hazard. If the battery being serviced can be charged with a simple charger, lithium and gel systems require compliance with a 2-stage combined energy storage mode.

All systems are designed to prevent overcharging and are equipped with automatic power off when the voltage required for a car battery is reached. When charging, the current gradually decreases due to an increase in resistance, but the voltage remains stable. After charging, the electrochemical reaction process continues in the form of a slight self-discharge.

It is important that the charging voltage always exceeds the parameters required for operating the device. For current to flow, you need a slope, which is the voltage difference between the charger and the battery.

We suggest you look at expert advice on how to properly charge and maintain a car battery, what voltage should be on the battery after charging.

We determine the degree of charge of the battery by voltage

The charge level of a car battery is measured when purchasing a new battery and if problems arise during operation. And if in the summer a certain discharge of the battery is acceptable, then as the temperature drops, difficulties may arise with power supply to the equipment or even starting the engine. Determining the battery charge level is a simple procedure that you can do yourself.

Normal battery charge

When purchasing a new power source, you should check the battery charge level, which refers to the amount of energy that the battery can produce over a certain period of time. That is why the battery charge is measured in Ampere-Hours. To obtain the most accurate readings, it is worth taking several measurements: without load or with it.

For a new battery, the potential difference level must be greater than 12 volts. If the car battery voltage drops to 10.8V, then using such a battery is not recommended - it should be charged. After the battery is fully charged, the voltage reading will be approximately 12.6 volts. The electrolyte density of a fully charged battery is approximately 1.28 g/cm3.

How does the voltage change when the battery is discharged?

The direct connection of parameters such as voltage and state of chemical elements (electrolyte and plates), as well as the charging level, affects the performance of the entire system.

After a car battery is fully charged, the electrolyte has a high acid concentration and the battery voltage is at its maximum. During operation, the density decreases, and therefore the voltage value drops, hence the battery charge. It is worth noting that the potential difference of the power source changes not only from the battery charge, but also from the number of devices connected to the network.

The relationship between battery charge and battery voltage can be seen in this figure:

The voltage and capacity of the battery are closely related. The manufacturer indicates both parameters in the power supply model. They show how much energy the battery produces over a certain discharge time. High currents and rapid discharge reduce the capacity of the power source, while lower ones can help increase this indicator.

It is customary to check the remaining battery capacity:

• by voltage under power using a load plug and direct current;
• spectral analysis;
• instruments that take readings at alternating current.

All these methods are based on information about the battery resistance, which allows only a qualitative assessment of the condition of the power source. The dependence of battery capacity on voltage is not a reason to determine battery performance. This is due to the possible presence of a floating charge, which will give a completely normal diagnostic result, which will not correspond to reality. Therefore, we recommend checking the residual capacity of the battery from voltage with the help of specialists who will conduct a computer study of the battery.

How to measure battery voltage correctly

The most accurate values ​​can be obtained by performing a set of diagnostics. To do this, you need to have special devices with you (multimeter, voltmeter or load plug). To measure voltage from the battery, it is necessary to connect the contacts of the device and the battery terminals.

During diagnostic procedures, it is worth understanding that the power source connected to the vehicle’s on-board system consumes energy. Therefore, the readings may be slightly lower, but they should not fall below 11-11.5 volts. Carrying out correct measurements is permissible on a completely disconnected and charged battery, that is, the electrical circuit must be open. However, this is an optional condition: if you check the voltage in a closed circuit, then take into account a certain error.

1. The battery is connected to the system of a car that is not started. Under this condition, the on-board network consumes a certain amount of energy, so the voltage indicator should be in the range of 12.5-13.0 V.
2. With the car running and the energy consumption sources turned off, the device readings should vary between 13.5 and 14 volts. Higher readings indicate that the battery is discharged and the generator is not operating normally. It is worth considering that an increase in data in the cold season is not an accurate indication of a low battery. If the voltage is within limits for some time, then the system is fully operational. Reduced readings (from 13 to 13.4 volts) indicate some discharge of the battery. Battery needs charging.
3. With the car running and power consumption sources turned on, the voltage value should be greater than 12.8-13.0 V.

Please note that working with a multimeter or voltmeter allows for an inverse relationship between the poles of the measuring device and the battery terminals. The load plug must be used strictly in accordance with the polarity.

We do not recommend checking your car's battery voltage using the on-board system because it is not directly connected to the battery. Therefore, certain measurement errors are allowed.

Checking the battery charge by voltage is recommended some time after the car battery is fully charged, as well as at operating temperature (about 20 degrees Celsius).

Below is the table “Battery charge level by voltage”.

Battery charge level

Open circuit voltage of low-antimony (Sb/Sb) and hybrid (Sb/Ca) batteries, volts

Accumulator charging.

Charging a car battery is the process of fully or partially charging the battery using a special charger; this process is not as simple as it might seem at first glance. This article will discuss the rules for charging car batteries using acid batteries as an example. But first, let's look at the components of chargers.

How to charge the battery by charging.

Charging a car battery is, in fact, a charger (charger), an electricity converter that charges electric batteries from an external energy source. The simplest chargers include only two elements - a step-down transformer and a diode bridge. The alternating voltage (220V) entering the memory is converted into direct voltage (15V), due to the transformer and diode bridge. This voltage is enough to charge a acid battery.

Electrolyte density, g/cm. cube (+15 degrees Celsius)

Voltage, V (no load)

Voltage, V (with load 100 A)

Battery charge level, %

Electrolyte freezing temperature, gr. Celsius

The design of the charger very often includes additional sensors (ammeter and voltmeter) and regulators (voltage and current). They help to more accurately select the voltage for each individual battery. Although there are already chargers with automatic adjustment, which themselves adapt to a specific battery.

Battery charging conditions.

What conditions must be taken into account when charging the battery? These are simple parameters that must be taken into account. Before charging the battery , you need to consider a few simple parameters:

• The optimal current for charging is 10% of the nominal capacity of the acid battery. For example, if the battery capacity is 80Ah, then the charging current should be 8A.
• The voltage at the charger terminals should be 10% higher than the battery voltage. Those. if the voltage at the battery terminals (it must be fully charged) is 12.6V, then at the charger terminals it should be 13.86V.
• To quickly charge the battery, you need to use electricity with a current of 20-30A. But, it is not advisable to carry out such charging, as it greatly damages the battery.
• When charging a gel battery, the voltage must not exceed 14.2V. This indicator is critical for the battery.

Now let's move on to charging the battery .

Home battery charging.

Home battery charging is the process of charging a battery using a special charger at home . Before you start charging your battery at home, you need to make sure that the battery is intact and really discharged. Therefore, it must be carefully removed from the car and cleaned of dirt. Next, you should carefully inspect its body for the presence of cracks. If there is one, this means that there is no electrolyte inside (it has leaked) and it is not possible to use the battery.

determine the level of battery discharge by the color of a special indicator that manufacturers install on the case cover. Different batteries, in turn, have different indicators, so you need to pay attention in advance to the explanatory sticker, which in most cases is located somewhere nearby on the cover.

The battery charge can also be checked by the voltage at the terminals using a conventional tester. If the battery is discharged, the voltage will be lower than rated.

You should also check the electrolyte level through the filler plugs. It must be clean and free of impurities, and its level must cover the plates. If the plates are visible, you need to add distillate.

Before you start charging, you need to clean the ventilation hole in the battery cover.

Charging the battery with a charger.

The battery is charged with a charger outside the living room, as the electrolyte evaporates. Also, the charger is first connected to the battery and only then connected to the electrical network. This must be taken very carefully, since incorrect connection will lead to failure of the memory fuses.

The battery can be charged in two different ways:

1. In the first case, charging can be done at a constant voltage value (14-15V), changing the current strength. Those. at the beginning it can reach 20-30A, but as the battery charges, it should decrease.
2. The second option is diametrically opposite. The current is a constant value, but the voltage varies. This method is more complex, as it requires certain knowledge and skills.

After charging, you can check the voltage at the battery terminals. This can be done using a load fork. If you don't have one, you can simply place the battery in the car. A charged battery will start the power plant and turn the starter without any problems.

Voltage measured at the battery terminals, V