How to determine if a car battery is charged

How to check the charge of a car battery at home?

The battery is the most important thing in any car. It is this element that provides the starting current to the starter. It is thanks to the battery that the engine starts quickly and without problems. But this doesn't always happen. To avoid difficulty starting, you need to periodically check its charge level. There are several ways to do this.

How to check the charge of a car battery at home? You will find out the answer to this question further in our article.

There are several ways to check the charge of a car battery:

by indicator;
using a loading fork;
multimeter;
by measuring the density of the electrolyte.

Each of them has its own characteristics. Let's look at the listed methods in more detail.

Built-in indicator

Most imported batteries have a built-in indicator that can be used to check the charge. For the first time such batteries appeared in Japan. Then European manufacturers began to practice a similar trick.

What is its essence? There is a transparent window on the battery cover (a kind of peephole). If you look at it, you can see that it is colored green. But this doesn't always happen. The green tint in the window will only appear if the battery is fully charged. If the window is transparent or white, it means the battery has lost part of its charge. The worst case is a black window. In this case, the battery has run down and needs to be charged urgently.

For your information, this is one of the easiest ways to check the charge of a car battery without a voltmeter and other devices. After all, all you need to do is open the hood and look through that very window. But it is worth noting that not all batteries have such a peephole (especially when it comes to domestic ones). Therefore, to determine the charge level, you need to know other methods.

Load fork

This is perhaps the most professional way to check the condition of the battery. Typically this method is used at service stations. What is its essence? The device is connected to the battery terminals and provides short circuit current.

That is, the load fork simulates the operation of the starter and shows how many volts the battery drops when the driver tries to start the engine. To date, this is the most accurate scheme for checking the condition of the battery. To read the readings correctly, remember that after loading the battery voltage must be at least 10 Volts. If the battery drops to 9 and below, it means it is already weak. Such a battery will discharge quickly in winter.

We use a multimeter

This is an indispensable device that every motorist should have. Allows you not only to check the battery voltage level, but also the resistance of the sensors, the load of the on-board network in real time and many other important parameters. You can purchase this device for 300-700 rubles, which is 2-3 times cheaper than a load fork. This device is very easy to use.

How to check the charge of a car battery with a multimeter? First you need to assemble it. We perform the following actions:

We connect two wires with positive and negative polarity to the corresponding connectors.
There will be probes at the ends of the wires. We apply them to the battery terminals.
First, set the device to voltage measurement mode and set the rotary switch to 20 Volts.
We connect the multimeter leads to the battery and look at the result. In this case, the car ignition must be turned off.

Reading data from a multimeter

What is normal for a battery? Experts note that a fully charged battery must produce a voltage of at least 12.5 Volts. If the multimeter shows exactly 12V, it means the battery is half discharged. A reading of 11.5 Volts or lower indicates that the battery urgently needs to be charged.

Electrolyte

There is another way to check the charge of a car battery with your own hands. It is especially relevant on the eve of winter. As is known, with a drop in temperature, the density of the electrolyte decreases. Accordingly, the charge and performance of the battery decreases. How to check the charge of a car battery? For this we need a hydrometer. Below are detailed instructions:

So, open the hood and, using a negative screwdriver, unscrew the battery “banks” one by one. There are only 6 of them.
We immerse our hydrometer inside and wait until it is filled with electrolyte.
Next, we take the device out and look at the readings.
After a short time, the float will float to the desired level. There will be several divisions on the scale. A figure of 1.23-1.27 grams per cubic centimeter is considered normal. If the electrolyte density is 1.2 grams, then the battery is about a quarter discharged. A deep discharge is indicated by a reading of 1.1 or less grams per cubic centimeter.

It is also worth checking the electrolyte level itself in each of the “cans”. If it is insufficient, it should be renewed. This can be done with distilled water (coolant is also diluted with it).

Do not ignore insufficient electrolyte level in the battery. This can cause frequent loss of charge and shedding of lead plates. As a result, the battery will become unusable, and during any attempts to recharge, the liquid will boil.

How to check the charge of a car battery with a charger?

Each charger has a scale that determines the battery voltage. If you don’t have a multimeter, a load fork and a hydrometer, you can use them. How to check the charge of a car battery in this way?

Everything is very simple - we connect the charger terminals to the battery terminals and press the test button. There is no need to connect the device to a power outlet - in this case it will charge, and the readings will not be lower than 13 Volts.

Can I charge at home?

If there is no garage, it is possible to recharge the battery in the apartment. But it’s better to do this on the balcony. During this process, the electrolyte releases sulfur dioxide and oxygen chloride, which are harmful to humans. Inhaling it may cause dizziness and nausea. Therefore, we charge in the most remote and well-ventilated area. Also monitor the electrolyte condition.

Do not allow the battery to boil. This reduces its resource. On average, a 60-amp passenger battery charges in 7-8 hours. In this case, the charger must be set to the minimum current strength. Stress loads are harmful to the battery. If the battery takes a long time to charge, or one of the cans boils after half an hour, it means it has become unusable.

Finally

So, we found out how to check the charge of a car battery. One of the easiest ways is to use a multimeter. As for the hydrometer, this is already a preventive measure. Yes, such a device can measure the “remaining life” of the battery. But, for the most part, it is a diagnostic device (as well as a load fork). Therefore, each device is good in its own way.

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.

How to properly charge a car battery

Experienced drivers are familiar with the situation when, when trying to start the engine, it turns out that the starter turns weakly. To restore the functionality of the vehicle, you will need to charge the car battery. It is important to carry out this operation correctly, not forgetting simple precautions.

How often to charge your car battery

In the automotive industry, acid-type batteries are used; they can be serviced or maintenance-free. First, you can independently check the level and density of the electrolyte solution. In a working car, the battery is constantly recharged. This function is performed by the generator. The relay-regulator process controls the process, through which the voltage supplied to the terminals is supplied.

If the generator unit is working, the battery capacity is sufficient and the outside temperature is positive, recharging is not required. If the relay is faulty and under difficult climatic conditions, the battery will receive insufficient voltage and will begin to gradually discharge.

At negative temperatures, the battery capacity decreases, so standard charging is not enough. In addition, in cold weather, engine oil becomes thicker and the battery experiences increased load during startup, and it does not have time to be fully recharged.

Therefore, the recommended charging frequency with working equipment is once a year in late autumn. If part of the battery capacity is lost or the relay-regulator gives a charge less than normal, then recharging should be carried out as needed.

If the ignition system malfunctions, you have to turn the starter for a long time when starting. This requires energy consumption and causes the battery to drain quickly, so you will have to use the charger often.

Checking the car battery

Most modern models have an indicator on the top cover of the case. The design of this indicator is extremely simple: a green spherical float floats in a glass flask.

If the density is sufficient, the float floats up and can be seen in the indicator window. When the battery is discharged, the density of the electrolyte in its banks drops, the ball drops down and is not visible.

However, not all batteries have such an indicator, so you have to use other checking methods. One way is to use a multimeter. This device measures the voltage at the terminals. The measurement results are compared with the data in the table:

Charging the battery or how to properly charge a dead battery

It is worth noting that old batteries (5 years old) should not be charged or reanimated using any old-fashioned methods. Firstly, it is useless or will only give a short-term effect, secondly, it is unsafe. Its life is coming to an end, and it would be wiser to recycle it.

Charger requirements. Batteries that do not need to be topped up with water should be charged only with devices that automatically maintain the charging voltage, and preferably automatically limit the charging current. Naturally, OBSERVE THE POLARITY OF CONNECTING THE CHARGER AND BATTERY! THAT IS “PLUS” to “PLUS”, “MINUS” to “MINUS”! (after all, not every charger has “foolproofing”)

DON'T FORGET THAT THE ROOM SHOULD BE VENTILATED, because the gases released in this case are harmful to health, and arsine, sulfur dioxide, hydrogen chloride are also released, which, when mixed with oxygen in a certain proportion, forms an explosive mixture (well, if you suddenly want to set up a battery charging station, and simultaneously charge a dozen batteries :))))

The costs of purchasing an automatic charger are not justified, so it is better to look for WHERE you can use it once. A good device will determine the condition of the battery and select the required charging current. An excellent charger on the Internet will cost around 6-8 kilorubles, for example, ctek.ru/podbor.php?dev_id=105. And don't forget to clean the battery from dirt before experimenting with it. Dirt on the battery will conduct current (bypass the charging circuit), which is not good at all. And also, the battery begins to more or less accept a charge only after the electrolyte has warmed up to a positive temperature, so when you bring the battery home from the cold, let it “settle” or warm up, as you understand better.

The difference between serviced and non-serviceable is the availability of plugs for filling electrolyte. The developers made sure that this was not necessary. However, in a non-serviced one, it is possible to remove the cover and get to the plugs. But, as a rule, there is no point. It lasts for a lifetime. Yes, any maintenance-free battery should have holes on the sides to vent gases and normalize pressure.

When charging a maintenance-free battery, DO NOT allow the voltage at its terminals to rise to more than 15.5 volts.

The point here is in the physics of the process. The battery itself will take as much current as it requires to charge. Just for charging. What you push into it beyond that, by increasing the voltage, it will send mostly for electrolysis of the water that is in the electrolyte, and a little more for heating. That is, it will simply decompose water into oxygen and hydrogen at your expense. Distilled water is not in short supply. But you cannot add it to a maintenance-free battery. The amount of electrolyte will decrease irreversibly, and its density will also increase irreversibly (the water is gone, but the acid remains!)

There is another danger - if your battery is heavily discharged (the so-called “deep discharge”) and all the acid has gone into the plates, then you CANNOT start charging it immediately with the rated charging current. There is water between the plates and you will simply electrolysis it.

Therefore, if the battery is charged with a current of tens of amperes, in a short time, the charge will “stick” to its surface and will not allow the electrolyte to penetrate into the thickness of the plates. And in the case of charging with a low current - a few amperes - it will restore the charge throughout the entire thickness of the plate. The term "charge" - here somewhat formal - is the nature of the distribution of lead sulfate throughout the thickness of the plate.

1) Determination of charging current. The charging current should not exceed 1/10 of the battery capacity. For example, if you are interested in how to charge a 12 V 55 A/h car battery, then be sure to keep in mind that the charging current should not exceed 5.5 A. If the battery is deeply discharged, you need to charge it with a small current (1.5 - 2 ,0 A). If you are sure that the battery has not been deeply discharged, connect it to the charger, observing the polarity (see above). The charger (charger) must be in the off position. If the device has a voltage regulator, set it to the minimum voltage. Turn on the charger. Set the charging voltage to 14.4V. The process has begun.

2) During the charging process, the current will decrease. The process will end when the voltage at the terminals is 14.4V and the current drops to 200mA (i.e. 0.2A). It is impossible to overcharge or damage the battery with this voltage. The charging current will simply drop to the value of the self-discharge current of the battery.

IMPORTANT: A current that can be considered safe for a battery is numerically equal in Amperes to about 1/20 of its capacity in Amperes/Hours, that is, for a 55 Ah battery this is a current of 2.75A. A current exceeding 1/5 of its capacity in Ampere/hour can be considered dangerous, that is, for a 55 Ah battery this is a current of 11A. Strictly speaking, when she can, she herself will “eat” even more - but only in certain modes and from the same 14.4V at her terminals. But if you use the handle of the charger to increase this voltage and overclock it so that 11A comes through the battery - it will most likely be far from 14.4V... PROHIBITED! The rated charging current has traditionally been considered for half a century to be a current equal to 1/10 of the battery capacity in Ampere/hours, that is, for a 55 Ah battery this is a current of 5.5A. For maintenance-free batteries, the main charging characteristic should be considered not current, but VOLTAGE. The current helps evaluate the process occurring in the battery.

3) In the case of a deep discharge, in this case it is necessary to charge the battery with a reduced voltage (12V.13V), and at the same time it is necessary to ensure that the current at the beginning of the charge does not exceed that same 1/20 of its capacity in Ampere/hours (in principle, this should happen automatically, unlike the situation when 14.4 V is immediately supplied to the terminals). If there is more, reduce the tension even more. The current will gradually increase - this is normal. This acid comes out from the depths of the plates, lead sulfate gives an influx of acid, the density of the electrolyte increases, and the battery is charged. When the current rises to 1/10 of the battery capacity, or even more, and it’s very good - when after this rise it even begins to decrease - then you can switch to the charging process described above, i.e. set the voltage to 14.4V.

Now for more information

for those who doubt it, like “why should batteries that do not need to be topped up be charged only by devices that automatically maintain the charging voltage?”

When charging using this method (charging at a constant voltage), the degree of charge of the battery at the end of charging directly depends on the magnitude of the charging voltage that the charger provides. So, for example, in 24 hours of continuous charging at a voltage of 14.4 V, a 12-volt battery will be charged by 75-85%, at a voltage of 15 V - by 85-90%, and at a voltage of 16 V - by 95-97%. The battery can be fully charged within 20-24 hours with a charger voltage of 16.3-16.4 V. Therefore, in OUR case (maintenance-free battery) for a satisfactory (90-95%) charge of modern maintenance-free batteries using commercially available chargers devices with a maximum charging voltage of 14.4-14.5 V will require more than a day. And to fully charge a battery of this type will take longer than to charge a low-maintenance or regular one. At the beginning of the charging process, the current sometimes reaches 40-50A, and therefore all chargers must be equipped with circuits that limit the charging current within 20-25A. The charging time depends on the level of discharge and can take up to THREE days.

How to determine the state of charge of a maintenance-free battery and its density

This is most likely impossible to determine 100% accurately. It is possible only with some degree of probability, or approximately. The method for determining the degree of charge by voltage is valid only for batteries that have been in a stationary state for at least 8 hours. The measurement must be made no earlier than 8 hours after turning off the engine. For a fully charged battery, the value is 12.7 - 12.9 Volts at a temperature of +20...+25 °C.

It is NOT ALLOWED to operate batteries in UNDERCHARGED mode, i.e. when the mains voltage is below 13.9 Volts, and in OVERCHARGE mode, i.e. when the voltage on board is higher than 14.4 Volts. Therefore, check the charging voltage level at least once every 2 months.

The battery likes to live fully charged and in the cold (a cold battery has less self-discharge). If you put a charged battery on a constant recharge with a current equal to its self-discharge current, it will be 100% charged at any time, and there will be no harm to it from such a pastime. But on a car, it is better to have a maintenance-free battery charged at 90 or 95 percent. Then, if suddenly there is a voltage surge in the on-board network (failure of the regulator relay or something else), it, like a capacitor, has a chance to “gobble up” this surge. Moreover, without much harm to yourself, and at the same time saving electronics, which would otherwise begin to emit smoke.

If your car’s generator and relay regulator are in good working order, then you will never have more than 15.1V in the on-board network (the voltage of the thermal compensation circuit of the relay regulators can be raised to this value in cold weather). Therefore, when taking care of the battery, do not forget to periodically check the generator and relay regulator.

And remember! — Experience grows in direct proportion to the amount of equipment disabled...

How to check your car battery for performance

One of the important elements of a car that requires checking is the battery, or battery. The serviceability of the battery and its performance are very important, since it is thanks to the battery that the car starts, and all systems of the car are powered by it: low and high beam headlights, media system and much more.

Content

If you have already met with the seller and want to be sure that if you buy a car, the first thing you will have to do is run headlong to the store for a new battery, which usually costs more than 10 thousand rubles, then you have several ways to check the battery by car:

Inspect the battery externally;
Measure the voltage on the battery with a multimeter;
Check the battery with a load fork;
Check the electrolyte level in the battery.

We will consider each question in detail, but we immediately note that the fourth option, with checking the electrolyte level, is only available for serviceable batteries. But one way or another, there are a number of methods for checking a car battery for performance, and in this article we will look at them.

External inspection of the battery

You met the seller and have already walked around the car, seeing how clean and beautiful it is. It's time to look under the hood, you lift the lid and see the usual contents of the engine compartment, the engine and numerous systems that keep the car running.

In most cases, here, in the engine compartment, there is also a battery - a rectangular box with electrolyte inside, to which two wires are connected - positive and negative. These wires go to the distribution block, and from this massive electrolytic “battery” the entire machine and all its systems are powered with electricity.

Even if you don’t understand anything about cars and went for an independent inspection rather as part of a formality, you can still determine by the appearance of the battery what condition it is in.

During an external inspection, attention should be paid mostly to the integrity of the elements, and whether the battery itself and contacts are clean. There are a number of external factors, the presence of which immediately indicates the need to replace or at least clean the battery.

Dirt on contacts. In order for the battery to work, both contacts connected to it by wiring must be clean. If the contacts are dirty, this indicates that the battery is not new, and dirt will interfere with the correct operation of the contacts.
Oxidation of the terminals - foreign deposits can be seen on the battery terminals with the naked eye - this is oxidation, which in most cases is associated with electrolyte leakage. Electrolyte is an acid that is found inside the battery. If it spills and gets on the contacts, it can lead to poor battery performance and a reduction in the contact area.
Cracks on the case - the battery itself should be intact. The plastic box containing the electrolyte must not be damaged. This is also clearly visible without additional equipment and in good lighting.
Dirt, dust, electrolyte leaks - all this is removed with a rag, and the car should not be allowed to drive with a dirty battery, since the conductive deposit will contribute to its rapid discharge and deterioration of performance.

In addition to the external inspection, you can start the car engine. A cold start will be especially indicative if the engine has not been started for a long time and it is cold outside. If the car starts easily, the battery is in order, but if it does not start or starts with difficulty, the headlights shine dimly, and the instrument panel is also not brightly lit, then the battery should be changed. Or, at least, check it with instruments, which we will discuss below.

Measuring voltage with a multimeter

If you do not want to check the condition of the battery “by eye”, or simply want to have accurate results in numerical terms, you will need a device such as a multimeter.

So, how to check a car battery with a multimeter: the device itself has two probes, one of which is red and the other black. In order to measure the voltage on the battery, you need to put the multimeter in measurement mode and place the red probe against the “positive” terminal, and the black probe, respectively, against the “negative” terminal.

The procedure is carried out on the battery terminals without load. If the battery is properly charged, the result on the device will be about 12.6-12.9 volts. This is the normal voltage that should be present on a fully charged battery. If you mess up the colors of the probes, the number will be the same, it will just be displayed with a minus sign.

If the engine is running, then you can also check the operation of the battery with a multimeter, but in this case it will be checked whether it is working together with the generator, as well as the serviceability of the voltage regulator. When the motor is running, the readings should be slightly higher - from 13 to 14 volts. If the indicator is lower, this will mean charging problems for the battery, and if the indicator is higher, the process of water electrolysis will begin.

There is a method to determine the degree of battery discharge by voltage. Voltage 12.5 - says that the battery is 90% charged, voltage 12.1 - 50%, and 12 - 10 percent. Although the method is approximate, it is proven.

It is also advisable to measure with the device “cold”, since a car that has recently been running can give higher values and be misleading. The multimeter checks the degree of charge, but does not provide comprehensive information about its performance. To do this, it is better to use a load fork.

Checking the battery with a load fork

The load fork is a very precise tool, but is rarely used in “manual” use, as it is used mainly in service stations. The beauty of this method of verification is that thanks to it an absolutely accurate result will be known.

The load plug works in a similar way to a multimeter: it is also connected to the battery terminals, but produces a short circuit current. As we already said, without load the indicator should approach 13 volts. The load fork imitates the operation of a starter, which is why the voltage “sags” at the moment of use.

The drop should be no more than 9 volts. Otherwise, it will mean that the battery is very discharged. After removing the load, the indicator again “rolls back” to its original value. If under load the voltage “sags” to 5 or even 3 volts, this means that the battery will not be able to start the car engine.

It is recommended to think about changing the battery even if the voltage when using the load plug drops below 9 volts.

An extremely important note: the load plug supplies approximately 200 amps of voltage to the battery and is not recommended for use in low temperatures. The ideal conditions for “field” use of this device is a temperature of +20-25 degrees Celsius.

If you apply voltage to a cold battery, there is a risk of severely discharging it.

Checking the electrolyte level in the battery

Another convenient and reliable method, which, however, is only suitable for checking serviced batteries, is checking the electrolyte level. The method is a little more complicated than the previous ones, but it gives a good idea of the condition of the battery and tells you what’s inside it.

First, remove the battery and completely clean it of dirt. Let us remind you that it is better to do this with a rag; dirt and minor corrosion can also be cleaned off using an ammonia-based glass cleaner.

Next you need to open the two filler plugs. They need to be easily pryed with a screwdriver and unscrewed; six filler holes are hidden under them. The electrolyte level in them is checked by eye and can be seen with a flashlight. If the liquid level is the same everywhere, then everything is in order, if somewhere the liquid does not cover the plate, you need to add distilled water.

In general, this procedure must be carried out regularly, since each time the battery is charged, the electrolyte decomposes in small proportions into hydrogen and oxygen. Without regular maintenance, the battery will simply fail.

The norm is considered to be a level exceeding the height of the plates by about one centimeter, or below the neck of the filler hole by three millimeters. If necessary, it is worth adding distilled water to the battery being serviced, but we remind you once again: if the battery is marked “maintenance free”, or the manufacturers of this particular battery model do not recommend adding distilled water to it, you can only resort to the previous testing methods and, if necessary, replace the battery.

Knowing how to properly check a battery is important when buying a used car. Often, car sellers want to save money on small things, including selling a car with a dead battery, which can lead to negative consequences for the new owner. Always be alert and fact-check what the seller says about the health of your car.

And don't forget to check the car's history before purchasing. This can be done using the Autocode online service using VIN or state registration number. number. The system checks the car in more than 12 official databases: traffic police, EAISTO, RSA, taxi and bank registers, Federal Tax Service, Federal Customs Service and others. From the report you will find out: actual mileage, whether there are traffic police restrictions, compulsory motor liability insurance data, customs history, history of fines, participation in road accidents and much other important information.

If you do not have the opportunity to go for an inspection or you simply doubt your experience, order the Autocode on-site inspection service. An expert will come for an inspection and conduct a comprehensive diagnosis of the car, leaving no doubt about your choice of vehicle.