How to determine if a car battery is charged

How to properly charge a car battery

The battery is one of the most important parts of a vehicle: it allows you to start the engine and replace the alternator if it malfunctions. Recharging a car battery can be done with a working generator device (in the car) or from a charger (indoors).

To extend the battery life and avoid damage, you need to choose the right car battery charging parameters and follow safety precautions.

How often to charge your car battery

The frequency of charging the battery is determined individually. The battery consists of 6 sections-cans that contain the electrolyte reagent and electrodes. The most common type of car battery is WET. It uses acid as a reagent and lead as a material for electrodes.

During operation, the battery capacity decreases due to several factors:

contamination and reduction in reagent quality;
acid evaporation;
sulfation of lead electrode plates.

Reducing the battery capacity increases the required charging frequency, but shortens its duration. When using the battery for a long time, it is recommended to regularly check the voltage of the device.

The normal battery charge value in the warm season is >50% of the nominal value, and in the cold season - >75%. This is due to the difference in electrolyte density, the load on the battery and the degree of risk of it turning off at different temperatures.

Motorists and service center technicians recommend charging the battery to 100% at least 2 times a year, one of which is immediately before the onset of cold weather.

Checking the car battery

There are several ways to check the battery charge:

Using an indicator on the case. Some batteries are equipped with a hydrometric indicator. It allows you to evaluate not only the charge, but also the fullness of the reagent. When the indicator is green, the charge and acid level are normal; when it is white, the device requires recharging; and when it is red, the charge is at a minimum and/or the reagent needs to be topped up.
Using a multimeter. The diagnostic device is set to voltmeter mode and connected to the battery terminals. At the same time, the engine must be turned off: otherwise the driver will receive a charge from the generator, not the battery. When there is no load, the voltage at 100% charge is 12.66 V, at 75% - 12.42 V, at 50% - 12.18 V, at 0% - 11.7-11.8 V. Considering the small difference in indicators, The multimeter must have a minimum measurement error.
Using a load coil. This diagnostic device is a resistance element (18-20 mOhm), to which a voltmeter is connected in parallel. The coil is connected to the battery outputs for a few seconds, and then the readings are taken from the measuring device. Load tests are carried out mainly in car repair shops or at the point of sale of car batteries.

The charge level is measured no earlier than 8-9 hours after turning off the engine or removing the battery.

Experienced motorists identify an additional method of checking the battery: by ear. If the charge is at a sufficient level, the car starter rotates normally. When the charge decreases, the power system starts with effort, and the starter spins more slowly and with noticeable attenuation.

In service centers, the charge is often measured when starting an internal combustion engine (ICE) or lighting devices (dimensions and high beams).

When starting an internal combustion engine, the voltage norm is 9.5 V or more. If the voltmeter readings are below this value, this indicates a discharge of the battery or a malfunction of the starter. For differential diagnostics, a guaranteed working and fully charged battery is installed in the vehicle.

When measuring against the background of lighting devices, the battery voltage should be at least 11.2 V.

How to prepare a battery for charging

Preparing the device for charging is carried out according to the following algorithm:

Remove the battery from the car or disconnect it from the on-board network, disconnecting both wires or at least the negative wire. In the cold season, you need to bring the battery into a room with a temperature of at least +10°C and leave it for several hours so that the electrolyte has time to warm up.
Clean the terminals from oxides, sulfides and grease. Wipe the surface of the battery with a rag moistened with a solution of soda or ammonia (10%).
If the battery is a serviceable type, unscrew the caps located on the banks and place them next to each other. Drain off some of the electrolyte to check the color and presence of impurities. If the battery is maintenance-free, then remove the plug from the ventilation hole on the device. This will ensure the free release of reagent vapors and make the procedure safer.
Serviceable battery plugs allow you to add water to the sections. If the plates in the jar are immersed in the reagent by less than 0.5 cm, then it is necessary to add a little distilled water into it and level the level in other sections. This procedure is not carried out for a maintenance-free device, because the reagent remains at the required level throughout the entire service life.

Safety precautions

In the process of preparing and charging the car battery, the following rules must be observed:

charge the device in a well-ventilated area (garage, service station, or at least on the balcony);
if there are small children in the family, you cannot exercise in the apartment;
It is prohibited to smoke, set fire to anything or cut metal in the immediate vicinity of a charging battery;
Do not charge the device in a room with high humidity;
connect the terminals and clamps of the charger only when the charger is disconnected from the network;
use safety glasses and gloves during work to prevent the dangerous effects of acid fumes;
When working with a battery, keep a solution of 10% bicarbonate or sodium carbonate (soda) nearby.

A soda solution is suitable both for wiping the battery case from reagent fumes, and for neutralizing acid in case of careless handling of the electrolyte.

How to charge the battery

To start charging, you need to correctly connect the “crocodiles” of the charger to the “plus” and “minus” of the battery. In most cases, manufacturers mark the positive terminal in red and the negative terminal in black. However, before starting the process, it is recommended to clarify the polarity by finding the “+” and “-” signs on the battery case.

Connecting a battery to a charger under voltage may result in sparking at the terminals and ignition of gases that are released during electrolysis of distilled water.

There are 3 main ways to charge a battery: automatic, constant current (I) and constant voltage (U). They differ in duration and effectiveness. Despite the corresponding names, in the absence of automatic control systems, it is necessary to control both charge parameters (U, I).

You should check the battery charge level and temperature from time to time. When the reagent boils, you must immediately reduce I to recharge at low values.

DC charging

Charging at constant I is carried out as follows:

The current value is set at 1/10 of the battery's rated capacity. The standard capacity is 55 or 60 ampere hour. This means that I on the charger should not exceed 5.5-6 A, respectively. By manually setting this value on the charger, you must continue charging until the voltage measured at the terminals reaches 14.4 V (permissible error - 0.1 V).
When the battery is deeply discharged, it should be charged not with the nominal, but with the minimum I (1.5-2 A). This will avoid strong electrolysis of water and gradually increase the density of the electrolyte due to the decomposition of lead sulfate.
Once the specified U value is reached, the current should be reduced to 1/20 of the capacity. At 60 A*h it corresponds to 3 A. Reducing the charging intensity allows you to reduce the heating rate of the reagent and continue recharging to the maximum.
When U reaches 14.5-15 V, it is necessary to reduce I by half again. At the final stage of the process, you need to charge the battery until both charge parameters (I, U) reach a constant value. The final value of I should be within 0.2 A, which corresponds to self-discharge of the battery. The whole process takes from 8 to 12 hours.

Upon completion of charging, you need to allow the released gases to escape, wipe the battery case again with soda solution, tighten the caps on the cans or return the ventilation plug to its place.

If you neglect to neutralize the surface, the battery will quickly discharge again due to current loss to the electrolyte layer on the case.

Constant voltage charging

To charge at constant U you need:

Set the voltage to the nominal charging level - 14.4 V (permissible error - 0.1 V). Strict voltage control is necessary when charging maintenance-free batteries.
Observe the current value. It should be about 0.1 capacity (for maintenance-free batteries) or 0.05-0.1 capacity (for maintenance-free ones). I more than 20% of the capacity is harmful to the battery.
With a deep discharge, recovery should begin with U no more than 12-13 V. The value of I should not exceed 5% of the battery capacity. If I rises, then the voltage needs to be reduced even more.

Recovery at constant voltage is a longer process than at constant current. At nominal U, the battery restores 75-85% of its charge per day, at 15 V - up to 90%, at 16 V or more - 95-100%. In addition to these data, it is necessary to take into account the limitation of the charging voltage: for a battery U above 15.6 V is dangerous. If the discharge is severe, the recovery time for the device can be up to 3 days.

Accelerated battery charging

To quickly charge the battery, you need to apply I to it at 10-15 A, which corresponds to 20-25% of the device’s capacity. In 15-20 minutes of intensive recovery, the battery will acquire a sufficient charge to start the car.

Regularly using this charging method is harmful, because... High charger current shortens battery life.

Dependence of battery charge and electrolyte density

The charge and density of the electrolyte are interdependent quantities. If the battery is severely discharged, the driver will not be able to quickly restore battery function, because the reagent density in the sections will be minimal. The relationship between the density of the acid solution and the degree of charge of the battery is presented in the table.

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Is the battery charged? How easy is it to check?

No sooner had winter arrived than something became wrong with the battery, which had been working well for the last couple of years. You can feel him straining with all his strength, trying to revive the frozen car. And this is at ten to ten degrees below zero, or will it still be at twenty, as they promised this winter? How do you know if it’s time to do something with the battery so as not to be left alone with a cold car in winter?

Many people looking under the hood ask the question: How to check if the battery is charged? There is an old grandfather’s method, which almost every issue of the magazine “Behind the Wheel” wrote about. We buy a hydrometer at the store. This is a glass tube with a bulb and a float that needs to be put into the battery and the float should show whether our friend is charged.

Hydrometers are different, the float should indicate the state of charge of the battery

The hydrometer operates on the principle of measuring the density of the electrolyte; we use a bulb to collect the electrolyte from the battery, and the float sinks or floats depending on the density. On the float there is a scale showing the density and the corresponding degree of charge. Somewhere there was also a table that made adjustments to the readings if the temperature at the time of measurement differed from 25 degrees Celsius. The most accurate way to determine capacity, and also the most correct.

We carefully inspect the battery. To get a better look at it, I even brought the battery home. And so, we look and are surprised, and where is there something? By and large, most modern batteries are considered maintenance-free. (Maintenance-free means you don’t need to do anything with it for the first two or three years, and when you need it, it’s easier to throw it away and buy a new one) And there’s even a peephole to visually check the charge. For some reason I can't see anything through it.

With maintenance-free batteries, everything is considered to be sealed and sealed, but you and I understand that at the factory the electrolyte should have been poured into this standard acid battery somewhere. We look carefully and see that there are still holes, just unscrew them with a coin and you can check. But we will not test it with a hydrometer. Firstly, there is acid in the battery, and it will be very unpleasant if it gets, for example, on your finger. And secondly, you can understand the degree of charge of a 12-volt battery simply by measuring the voltage at its terminals and without getting dirty with acid. The method is of course less accurate, but there is no need to get dirty.

There are only two nuances here. The voltage should be measured a few hours after the last trip (charging) so that all chemical processes calm down. If you measure it right away, the battery will always show a very good result. You need to measure it with a digital voltmeter, which shows tenths, or even better, hundredths of a volt. Of course, if you are a big fan of car batteries, you can use the first option, with acid and pears, but I prefer the second. In addition, my alarm key fob shows the voltage on the battery, look in the instructions for your car, maybe you have something similar.

So: table of charged battery voltages

The good thing is that air temperature has virtually no effect on voltage. Those. In cold weather the voltage will be a little less, but not much. However, negative temperatures greatly affect the battery’s ability to deliver its capacity. Let's look at the table.

Approximate dependence of battery capacity on ambient temperature

If the battery is 100% charged at 25 degrees Celsius, then the lower the temperature, the less it can give up its capacity. But if the battery is discharged, say 50%, then when the temperature drops to -20, you can start the car only by calling a friend for help. And a discharged battery can simply freeze, turning into an ice barrel. Of course, you can thaw it and then try to charge it, but how it will all work later is unknown. It won't work well, if at all. So it’s better not to let this happen.

And at what voltage should the battery be charged? The answer comes from the car manufacturer. In some particularly advanced cars, if the battery voltage drops below 12 volts, for example to 11.9, which according to the first table is 40% of the capacity, then the car displays “Battery low” on the on-board computer. For me, for example, it starts making nasty noises every time I open the door, like, master, quickly charge me, my death will come soon. Of course, the manufacturer is playing it safe and you can still drive on such a discharged battery, but it’s still better to take the battery to a warm room for charging without waiting for a frost of 20 degrees.

We charge the battery using an automatic charger.

And in a warm time, so that the battery takes all the possible capacity, and not how much is indicated in the table.
The charger must be fully automatic, so as not to carry around with hydrometers to determine the degree of charge/discharge. I still have it from the old days and it works great, it even charges a 70A battery, although the instructions say that it works for 55-60 amperes.

Is it possible to recharge the battery at idle so as not to carry these 15-19 kilograms? Of course you can give it a little extra charge, the question is how long you need to run the car at idle speed. This time depends on many factors. But besides empirical arguments, let's look at the numbers. A car generator produces up to 80 Amps at a maximum speed of about 5000 rpm. At idle, the generator will produce about 30-40 amps. Is it a lot or a little? It all depends on the consumers. If the ignition circuit takes about 20 amperes, the headlights another 20, the glass heating 15. Of course, a little less, since we look at the size of the fuses.

But we still see that even with consumers turned off, almost all the current generated by the generator will be spent on maintaining the operation of the machine, and there will be nothing left to charge the battery, good if there are 10 amperes. With this current, a discharged 60 ampere battery will be charged in about 6 hours, and even if the battery takes a charge, we remember that in the cold the battery capacity decreases sharply. Here is the answer. And if you remember that the starter immediately takes 150-200 amperes, and maybe up to 500 amperes in a very slow-frozen version, then it’s not worth starting the engine again to “recharge” the battery. It’s better to take the discharged battery to charge somewhere warm and it will be fine.

How long do you need to drive for the battery to charge? If you have short trips, say less than an hour, and even around the city, where you spend more time in traffic jams at idle or close to idle, when we “stand slowly” in mode, then the battery in this case will gradually discharge. And after a couple of months, even a fully functional battery will need to be charged. In winter, the problem is aggravated by the fact that during short trips the cold battery does not warm up and simply cannot take a charge. In the summer, when the battery is warm, recharging begins immediately after the start of the trip, which clearly has a positive effect on the ability to start the engine.

The conclusions are simple:
Firstly, until the engine is started, it is better not to turn on additional energy consumers in order to save battery power.
For example, my car had such a function as “Polite light”, when after setting the alarm, for another 15 seconds the car helpfully illuminated me with low beam so that I would not walk home in the dark. Yeah, but she usually stands with her face towards the fence, and politely shines her light into the fence. And taking into account the fact that in order to disable this feature I had to specifically go to a service center and program the car’s brains, this thing drained my battery well until I turned it off. Secondly, there are fewer short trips; not only does the gas consumption go crazy, but the battery also runs out.
But that's how it goes. Thirdly, monitor the voltage on the battery. And if it drops below 12 volts, then don’t hesitate to charge the battery. And if it’s three years old or more, and it worked fine before, then either something in the car has worn out and is shorting out, or the trips are short, or maybe it’s time to change it; now it’s not that expensive.

How to properly charge a battery - useful tips “Behind the Wheel”

Filling a jar with electricity is an expression from V.I. Dahl’s dictionary: this is how he explained the meaning of the word “charge.” It fits perfectly into modern six-cell car batteries. True, the banks turn out to be different - both in design and in condition. How to fill them with electricity?

All batteries can be divided into low-maintenance, maintenance-free and completely maintenance-free. The oldest of them are low-maintenance, with gratings made of lead-antimony alloy, the coolest are completely maintenance-free, with gratings made of the purest lead. It should be noted that “maintenance-free” means extended intervals for adding water or the complete absence of this procedure throughout the entire service life. But any maintenance-free battery requires periodic monitoring along with other car components. Contrary to popular belief, there is no significant difference in charging these three types of batteries.

Should I charge it or not?

Is it possible to charge in the cold?

How to charge when traveling infrequently?

Charger or generator – which charges better?

Under normal operating conditions, a charger is not needed. The battery must be charged from the generator. And a charge at a constant voltage of a working car is the most correct and useful for the battery.

The task of a stationary charger is to restore the battery, albeit not completely, but enough for the generator to recharge to 100%. When charging with direct current, in order to avoid overcharging and “boil-off”, that is, the consumption of water from the electrolyte, the stationary charger interrupts operation at a level of 14.4 V, switching to recharging mode with a minimum current during storage. This usually prevents the battery from being fully charged. And the generator charges it in constant voltage mode.

Depending on the settings of the vehicle's power supply system, the voltage regulation range is 13.8–14.5 V. The charge current is determined by the internal resistance of the battery, which characterizes its current state, and decreases as the voltage at the battery terminals approaches the generator voltage. That is, a stationary charger produces a specific current in accordance with its algorithm, and the battery takes the current it needs from the generator. This is why a charger cannot charge as well as a generator.

What should the charge mode be?

When the NRC drops below 10.5 V, this is already an ultra-deep discharge. If the battery is drained in a short time, it can be quickly charged with a high current of 10–20 A (10% of the rated capacity) from a stationary device within a few hours. If the battery was chronically undercharged and died slowly, the charge must be started with a minimum current at a constant voltage. To do this you will have to contact a specialized service.

Should I remove the battery from the car to charge it?

Can I “light up” from another car?

Opinions on this matter often differ, but the debate is only about the safety of the vehicle’s electrical equipment and its compliance with the operating instructions. One thing is certain: the battery will definitely not be damaged! In our opinion, “lighting” is safe if a simple scheme is followed: we connect the positive terminals of the donor and acceptor to each other, and place the negative terminal of the donor on the body of the “lighting” car.

The editors would like to thank Dmitry Tishchenko, an expert from the National Association of Power Source Manufacturers, for his assistance in preparing the material.

The assortment of the Za Rulem online store includes inexpensive and time-tested chargers from the Tambov plant. A great gift for yourself and a fellow car enthusiast!

How to charge and check the battery charge

The main purpose of the starter battery is indicated in its name: it is a source of energy for the starter to operate. That is, the battery plays its main role at the engine starting stage, and then energy is supplied to the on-board electrical network from the generator.

At the moment the engine starts, the battery loses a significant part of its stored energy and needs to be charged - this is performed by a generator, which, in theory, should restore the battery in a relatively short time. However, this does not always happen, or rather, it rarely happens; in general, the batteries are either constantly undercharged (mainly in the city) or overcharged. In the first case, it is necessary to bring the charge to a normal level, and in the second, you should think about contacting a car service: overcharging may indicate a malfunction of the relay regulator. With constant recharging, the battery simply fails, and this, among other things, is not a warranty case; it will be impossible to replace the battery for free.

Battery diagnostics

How to check the battery? Based on what parameters can we conclude that the battery really needs to be charged and restored?

There are only two such parameters - voltage and electrolyte density. But if everything is simple with checking the first, then problems may arise with the second - now maintenance-free batteries are widespread, it is simply impossible to find out the density of the electrolyte in them. However, let’s not get upset in advance, but let’s see what can be done about it.

First you need to measure the voltage: at 100% charge there should be 12.7 V at the terminals, and the density of the electrolyte should be 1.265 g/cc. If the voltage is lower, then the battery is discharged: 12.4 V corresponds to a 75% charge, 12.2 V indicates a 50% charge, and a voltage of 12.1 V indicates that the charge is only 25%.

Checking the battery showed that it needs charging, what should I do next?

How to charge a classic car battery

It is easiest to charge a battery with a classic design - the presence of plugs and the ability to see the electrolyte allows you to control the charging process and achieve better results.

Before connecting the charger to the battery, you need to unscrew the plugs to open access to the electrolyte. Then you can proceed directly to charging, choosing one of several methods.

It is easiest to charge a battery of a classic design with a constant current. To do this, a current equal to 10% of the battery capacity is selected on the charger: if the capacity is 60 Ah, then the current will be 6 A. There is no need to set the voltage in this case - it will be automatically adjusted by the charger.

Now you need to show a little patience - a new battery can be charged in this way for up to 8 hours, a battery with “experience” gains a full charge in a longer time. And all this time (every one and a half to two hours) you need to check the voltage and density of the electrolyte.

Don’t be surprised that the voltage will be higher than the usual 12.7 V - that’s why the battery is charging. When the voltage reaches 14.4 V, it is worth halving the current. The electrolyte density should also constantly increase, but not too quickly.

How long does it take to charge the battery, and how do you know when it needs to be disconnected from the charger? This will be visible immediately, since the first sign of a full charge is the “boiling” of the electrolyte. The violent reaction is due to the fact that due to the battery being fully charged, the nature of the electrochemical reactions occurring in it changes. Specifically, water molecules begin to break down into hydrogen and oxygen, and these gases leave the jar, creating a boiling effect.

In this regard, remember about safety! Charge the battery in a well-ventilated area, and do not bring open fire to it - hydrogen mixed with air will ignite even from a spark, and can lead to a fire and even an explosion of the battery!

You can turn off the charger 15 - 20 minutes after the electrolyte “boils”, after another 20 minutes you can tighten the plugs - you need to let the gas escape completely.

But bubbling electrolyte is not the only sign of a full charge. The battery can be considered charged if the current, voltage and electrolyte density do not change within one to two hours. Then you can safely turn off the charger and put the battery back in place.

How to properly charge a maintenance-free car battery

It is best to charge a maintenance-free battery using another method (which, however, is suitable for any type of battery) - constant voltage charging.

In this case, a certain voltage is set on the charger, and the current will be adjusted automatically. More precisely, the current will change due to the laws of electrical engineering - as the voltage on the battery increases, the current will drop, and when the voltages on the battery and the charger reach equality, the current will become zero.

The latter circumstance determines the popularity of this charging method - it occurs automatically, since once a full charge is reached, no further charging is performed, which means there is no need to monitor the process.

However, this method has a drawback: it requires a lot of time - at least 20 - 24 hours. But even this time will not be enough if the charging voltage is set too low. So, at a voltage of 14.4 V, the battery will be charged 80% per day, at 15 V - 90%, and at 16 V - 95 - 97%. Full charging can be achieved at a voltage of 16.3 - 16.4 V.

This method is good because it allows you to easily maintain the battery in working condition, especially if the car is constantly operating in “taxi” mode. However, it is better to bring the battery to a full charge using the first method.

How to charge a car battery in winter

In winter, the battery operates under the most difficult conditions, since when starting the engine it is required to produce almost twice the starting current. But this is not so bad, because frost reduces the battery capacity, which means the starter can work normally for less time than in summer. So, at a temperature near zero, the battery capacity decreases by about a third, and at a temperature of minus 18 degrees, the capacity drops by half. Now it’s clear why the battery discharges in severe frosts.

But the battery charge level affects not only the car’s ability to start in cold weather, but also the physical condition of the battery itself. The fact is that the lower the charge, the higher the freezing point of the electrolyte. If the battery is fully charged, it will not freeze even at minus 60, but if completely discharged, freezing can occur even at zero degrees.

In this case, the electrolyte turns into ice and, due to the known properties of water, increases in volume. This leads to “inflation” of the battery, and sometimes the battery walls are completely destroyed. It must be said that this case is not guaranteed, so in winter it is necessary to monitor the condition of the car and use special winter oil - this will prevent the battery from being discharged by a long start-up due to thickened oil.

If the battery is not damaged by freezing, it must be warmed until the electrolyte is completely thawed and charged.

Fast battery charging

Sometimes you need to charge the battery very quickly, literally in two or three hours - is this possible? Yes, it is possible, as many car enthusiasts prove every day. Reducing charging time is achieved by simply increasing the charging current - in practice, the current is selected within 10 - 20 A.

It must be said that this method is not the best - too high a current contributes to rapid wear of the battery. But sometimes there is simply no other choice, and you have to risk the battery to save time.

First battery charge

In most cases, it is not advisable to immediately install a new battery in a car - it needs to be charged. But if you have a little time, but do not want to carry the battery home, then you can charge it from a car generator - just drive for at least an hour in moderate mode.

It is not allowed to immediately park a car with a newly installed battery in a garage or parking lot for several days - such idleness, especially in winter, will most likely lead to a discharge of the battery.

If you purchased a dry-charged battery, then in any case you will have to spend some time getting it into working condition.

How long does it take to charge a battery just bought in a store? As practice shows, from three to eight hours. You can charge it using any of the methods described above.

A dry-charged battery is another matter. First, you need to pour electrolyte into it, wait until the plates are saturated (this lasts from 15 minutes to an hour), then add electrolyte to the desired level, and wait - after about an hour and a half, the battery will charge, this can be seen by the “boiling” electrolyte.

When gas evolution stops, you need to check the battery voltage, and if it is lower than required, carry out normal charging using a charger. If the battery is new, then all this will take 3-4 hours, but if the battery has been in the store for over a year, then charging may take 6-10 hours.

Proper charging of the battery is a guarantee of its long and stable operation, and great attention must be paid to this matter. Moreover, with some skill this will not cause problems or inconvenience.

What is the charge rate of a car battery and how to check it

The battery (rechargeable battery or battery) is one of the key components of a car. The main role of a car battery is to supply current to the starter when the engine starts. In addition, when the engine is not running, the battery ensures the functioning of various devices (lighting, sound system, signal and other current consumers). When parked, the battery powers the security system. And during a trip, when the generator cannot cope with the load, the battery comes to its aid. Normal functioning of the vehicle's on-board network is only possible with a battery that has a normal charge. Therefore, today we will discuss what the charge rate for a battery is.

Battery charge rate

One of the main parameters of the condition of a car battery is voltage. Using voltage, a certain battery charge level is checked. Therefore, the car owner needs to know what the normal value of the battery voltage is.

The normal voltage of a six-cell battery in a charged state is 12.6-12.9 volts. That is, the voltage of one fully charged element is 2.1─2.15 volts. A lower value indicates that the battery is low.

But that doesn't mean it can't be used.
Ideally, of course, you need to keep the battery fully charged. But in practice, this can only be done if the battery is fully charged and then a current equal to self-discharge is applied to the terminals. So the battery is rarely in a fully charged state. Below you can see the relationship between voltage and battery charge level.

As for the charge rate, in most cases it is not recommended to operate a battery with a voltage of less than 12 volts. In this case, it needs to be charged. Operating the battery in this condition negatively affects the condition of the battery. This contributes to an increase in sulfation of the plates and, as a result, leads to a decrease in battery capacity.

The critical voltage norm can be called 10.8 volts. The voltage should not fall below this value. This is called deep discharge of the battery, which is very harmful to the battery and greatly reduces its service life. Deep discharge is especially harmful for maintenance-free calcium batteries. For them, 2-3 such deep discharges lead to failure. After such a voltage drop, they irreversibly lose part of their capacity.

As you saw in the table above, the density of the electrolyte is inextricably linked with the degree of charge. This is true. The charge level of the battery can be checked not only by the voltage at its terminals, but also by the density of the electrolyte. A fully charged battery should have a density value of 1.27─1.29 g/cm 3 . The density of the electrolyte is measured with a special device - a hydrometer. Read more about the electrolyte in the battery at the link provided.

EMF, like voltage, is measured in volts and represents the work expended on moving the positive charge between the terminals of the battery. Without electromotive force, there will be no voltage at the battery terminals. Voltage and EMF are present at the terminals of the power source, even without current flowing in the circuit.

What does this mean in practice?
Let's say you charged the battery and the emf at its terminals is 12.6 volts. After installation on the car and measuring the voltage, the value will be 12.4─12.5 volts. This is normal and there is no need to worry about it. Now let's talk about the tools for measuring battery voltage. We also recommend reading the article about why the generator does not charge the battery. Return to content

How to check the charge of a car battery?

To check the battery voltage, use a voltmeter or multimeter in voltage measurement mode.

In order to measure voltage with a multimeter, you need to switch it to voltage measurement mode. Then apply the probes to the battery terminals and the device will show the voltage value. Polarity is not necessary in this case, since you only need the magnitude. If you put the red probe on the minus and the black probe on the plus, the device will simply show a negative value. By the way, you can read more about what straight battery polarity is. But the photo below shows the result of measuring the voltage of a dead battery.

Voltage measurements with a multimeter

Before performing the test, the battery must be fully charged. To perform a load plug test, connect the terminals to the battery terminals and apply a load for five seconds. At the fifth second, note the voltage value on the voltmeter. If it drops below 9 volts, then it's time to think about replacing the battery. The norm for a working battery is a voltage drop to 10-10.5 volts. After the drop, the voltage value should increase slightly. In the video below you can see the testing process clearly.

In principle, there is another way to estimate the battery charge rate. You can measure the average density of the electrolyte in the banks, and then look at the degree of charge using the table above. But usually no one does that. It is much more convenient to use a voltmeter. The density of the electrolyte is usually measured after charging the battery to assess the efficiency of this process.

What to do if the battery charge is not normal?

The answer to this question is simple. If the battery charge is not normal, the battery needs to be charged. The charging process was described in detail in the article “How to properly charge a car battery with a charger.” Here I would like to note some nuances.

accelerated This mode is often called Boost and can be found on many modern chargers (chargers). In this mode, the battery charge is not fully charged, but it is quite enough to start the engine. This type of charging is used when you need to go urgently and the battery is low. This mode is not recommended to be used continuously. Here, the charge is accelerated by increasing the current strength, which increases the battery life;
with constant voltage. This type of charging involves maintaining a constant voltage across the terminals. This mode is used in the automatic charge mode on most chargers. It is recommended to use it when the battery is not very discharged (not lower than 12 volts). Read more about car battery voltage in the article at the link. The advantage of this mode is that you don't have to control it. The charger itself will determine when the charge is normal and stop the process;
with direct current. This charging option involves supplying constant current to the battery. The process is carried out in several stages, in which the current gradually decreases. This mode is recommended when charging a deeply discharged battery. It allows you to charge the battery most fully and evenly. The downside is that you will have to constantly monitor the process, measure the voltage and stop the process when the battery charge is normal.

Battery charging process

In conclusion, I would like to remind you about the safety rules when charging a battery. The process must be carried out in a ventilated area. It is better not to charge in residential areas. There should be no open flames or sparks near the battery being charged. During the charging process, hydrogen is released, which in combination with oxygen forms an explosive mixture!