How to test a car battery

Checking the car battery - when else can you fix it?

When the key is turned in the ignition, it is the battery that provides the impulse to start the engine. If the battery is completely discharged, the car is unlikely to move. It is for this reason that it is important to check the car battery in a timely manner (with a multimeter, for example), because problems noticed in time will not only allow you to avoid searching for someone to light a cigarette, but will also save you from much larger problems. Checking a car battery should be comprehensive and thorough and include both an external inspection and a check of the “inner world”, as well as electrical indicators.

Visual inspection

First of all, carefully inspect the battery: normally it is dry, clean and without signs of damage. It's bad when:

the surface of the battery is heavily contaminated;
terminals are oxidized;
the battery case is damaged;
There are traces of electrolyte.

Any of the items listed will lead to rapid discharge of the battery, and therefore increase the risk of getting into unpleasant situations. What to do?

The same solution will help deal with terminal oxidation - apply the mixture to contaminated areas, wait a couple of minutes and thoroughly clean with a brush (not a metal one!). After the procedure, rinse the cleaned surfaces with distilled water.

If the oxidation is extensive, then the first step is to resort to mechanical cleaning, the main thing is not to damage the wires.

Exploring the inner world

The battery check should continue with electrolyte measurements. It is he who is responsible for most of what happens to the car. The electrolyte is checked according to the following parameters: density and level.

To check the level you will need a glass graduated tube. Unscrew the washers covering the so-called banks - sections in the battery. Lower one end of the tube all the way down and close the upper end with your finger. Pick up the tube.

It is optimal if the solution covers the upper edge of the plates by 10–15 mm. The total liquid content should be 30–40 mm. So check each section.

The next step is to check the density of the electrolyte using a hydrometer. The normal value is 1.26–1.28 g/cc. see at above-zero temperatures. The indicator will be lower if measurements are taken at zero temperature, but this indicates a low battery charge.

If the density of the electrolyte is higher than the required values, and its level is lower, then it is worth adding distilled water. It is important that it is not any other water, since only the distillate does not contain impurities of salts and metals that can damage the battery.

If the density is slightly lower (1.24–1.25 g/cc), then the electrolyte is added. You can either make it yourself or purchase it in specialized stores. Excess liquid is removed using a “pear”. Any leaks of electrolyte must be removed from the housing!

Making electrolyte at home

For this recipe you will need a well-ventilated area, personal protective equipment (at least gloves), non-metallic utensils, distilled water and 360 ml battery (sulfuric) acid.

First, water is poured into the container, then acid is poured in small portions and carefully. The mixture is thoroughly mixed at all stages. Then the resulting mixture is left to stand for several hours, and the electrolyte is considered ready.

After the completed manipulations, but before repeated measurements, the battery must be charged using a low current. This is the moment when longer is better. After charging, the measurements are repeated.

If during measurements the readings differ in only one section, this indicates damage to the plates. Maintaining life in such a battery will cost much more than purchasing a new one.

Using a Multimeter

A common question is: “How to test a car battery for performance with a multimeter?” First, it’s worth understanding what is measured using this device:

Even the simplest multimeters will help in measuring air temperature and other indicators. Hence the name: “multi” translated as “many”, which means that the device can measure a lot of things. However, when it comes to the battery, it is the first three indicators that will tell you about its health. Let's take a closer look.

Voltage check

This manipulation will allow you to assess the current state of battery charge. To carry out the measurement, the multimeter is switched to the voltage measurement mode at around 20 units. Connect the red wire of the device (also known as “plus”) to the positive terminal of the battery, and the black (sometimes blue) wire to the negative terminal.

If the car is not started, then the optimal indicators will be numbers in the range from 12.4 to 13 V. In this case, a higher value indicates a 100% charge, and a lower value indicates an incomplete charge. It is better to carry out such a check when the car has been parked for a long time (at least several hours), in which case the measurement will be the most informative.

If the numbers are slightly less than 12, then the situation is bad - the battery is close to natural death. There is a chance to try charging it with a low current. Numbers close to 11 mean the death of the battery, and it is better to take care of purchasing a new one.

When checking with the car running, the readings will be different: from 13.5 to 14 V, the readings are good. If the figure is greater than 14.2 V, then we can judge that the battery is being recharged by the generator. However, if measurements are taken in winter, you should wait 15 minutes and repeat the procedure - perhaps the generator was intensively recharging the dead battery.

Capacity check

The battery capacity is usually indicated on the accompanying sheet. Another thing is that over time the capacity decreases, and it is important to keep track of this point. In this case, checking the car battery with a multimeter will be a good help.

To check, you will need:

disconnect the car battery from the generator;
connect an energy consumer with fixed consumption to the circuit (for example, a 12 V light bulb);
The operation of the circuit is observed for several minutes (here it is important to see whether the light of the light bulb becomes noticeably dimmer, whether there are any interruptions in its operation, etc.);
the consumer is switched off, battery readings are measured in voltage mode.

If the measurement result is 12.4, then this indicates that the battery is fully operational. If the readings are in the range from 12 to 12.3 V, then soon the battery may “forget how to work”.

Another method is the control discharge method. The steps are similar to the previous method, however, before starting the test, charge the battery to 100%, then connect a light bulb to the circuit, noting the exact time of switching on, and, under the control of an ammeter, wait until the battery charge is reduced by exactly half.

Next is the question of calculations: the time spent discharging the battery is multiplied by the current in the circuit. The result should be the same as in the technical passport or close to it. If this does not happen, then the battery capacity has already suffered greatly.

Resistance check

To understand what is happening, you can also check the internal resistance of the battery. To do this, you will need the same 12 V light bulb. It is connected to the battery terminals, and the voltage at the terminals is immediately measured. After the measurement, the light turns off and the measurement is repeated. If the difference in measurements is within 0.05 V, then the battery is working. If the difference is greater, then the battery has problems.

Checking with a load fork

To obtain the most accurate measurement results, a load fork is used. Of course, this equipment is rarely seen in private hands, much more often in professional workshops or at technical diagnostic stations. However, if it does exist, then why not use it.

The load plug is a device that, like a multimeter, is connected to the battery terminals. It then supplies a short circuit current to the battery, which simulates the operation of the starter. As you know, without load the readings are about 13 V.

At the moment of turning the ignition key, which is simulated by the load fork, the readings normally “drop” down. The maximum normal drop can be up to 9 V and return to the initial reading after the voltage is removed. In this case, the battery can be considered serviceable.

If the readings drop below 9 V, then even if they return to their original state, such a battery is unlikely to start the car. It is important to remember that testing with a load fork should be carried out only in the warm season (optimally at a temperature of +20... +25 degrees), otherwise it is possible to drain the battery charge during testing.

A little theoretical knowledge

Knowledge of how to test a car battery should also be combined with knowledge of normal values and readings and why they change.

The density of the electrolyte can change due to temperature fluctuations - overheating or hypothermia. In this case, in case of overheating, the electrolyte may boil, in which case the distilled water will partially boil away, and the electrolyte will become more dense.

In the case of cold, the electrolyte, on the contrary, often begins to have a reduced density. In both cases, the conductivity becomes worse, and therefore there are problems with the establishment, rapid “landing” and work on its last legs.

But why is any liquid so important? The thing is that the battery only looks like a small box. In fact, it consists of many parts, the main of which are conductive plates, positive and negative, which make up 6 elements connected in series. They are in contact with the electrolyte, so the electrical impulses move with the necessary force.

For what other reasons could a battery suddenly stop working? For example, just from time to time. On average, batteries work stably for 3–4 years. Of course, many work longer, but their capacity and ability to hold a charge still decreases.

Another reason is frequent battery overcharging, undercharging, or complete discharge. It is very important for a car battery to maintain some kind of average state, without strong changes.

The next reason is hidden in the generator, or rather, in its breakdown. In this case, it may either constantly recharge the battery, giving too much current, or, conversely, may not even be able to maintain the existing charge. Both options indicate the need for urgent replacement of the generator.

The last on the list of unpleasant situations is current leakage: something in the car consumes too much energy even when the car is turned off and parked. This can be determined using the same multimeter. To do this, you will need to turn off the car and remove the negative terminal of the car from the battery. Turn the multimeter into current measurement mode, set the switch to 10 or 20 units. Connect one wire to the negative terminal of the car, and the other to the negative terminal of the battery.

Conclusion

Simple car diagnostics are available to any car owner. Careful attention to the battery will save a lot of effort and nerves, especially on long trips, in winter or at low temperatures.

The simplest thing that anyone can do is remember to inspect the battery every time you lift the hood. Quickly inspect the integrity of the case, wipe it with a rag to remove dirt, make sure that the terminals fit tightly and there are no signs of oxidation.

Once a month it is a good idea to check the level and density of the electrolyte, this is especially true in winter, during severe cold or long trips.
If suddenly the car begins to behave strangely when starting up, the starter turns sluggishly, and the engine does not start the first time, serious problems are not far off, and you need to check both the battery and the car’s alternator in the near future. To do this, you will need a multimeter, which can be purchased at almost any auto store for a fairly modest amount. Timely attention to detail often helps to avoid serious troubles.

Battery check

The battery is the most important component of a car. Without it, the car will not start, since the engine is started by the starter, which in turn is powered by the battery. Checking the battery is necessary if the car does not start. Let's consider all the symptoms, malfunctions and diagnostic methods for serviceability.

You can check the battery in different ways. If the car cannot be started, first of all you need to check the voltage on the battery. It should be >12 V when the car is off and > 13.5 V when the car is running.

Methods for diagnosing a car battery

Let's consider the main methods for checking the technical condition of a car battery:

Terminal voltage. A multimeter is a device for measuring current and voltage. Can be used at home.
Diagnostics using a Postolovsky oscilloscope. USB Autoscope is a professional device for checking electrical signals in the engine and additional equipment, including the battery. For this purpose, Andrey Shulgin has developed a special ElPower script that can detect battery faults and charge level.
Checking with a load fork. The most informative device for measuring voltage under load.
Checking the electrolyte level. It should be 10-15 mm higher than the plates.
Electrolyte density measurement. A hydrometer is used for this.
Check battery capacity. On the case there is information about its capacity. The year of issue is written in the passport.

The average check price varies from 300 to 500 rubles, depending on the make of the car.

Battery diagnostics using a Postolovsky oscilloscope

Check the car battery charge with a multimeter

If the starter turns poorly or the car does not start, the first thing you need to do is check the battery charge. This service is available at a car service center, but to do this, the car will have to be transported on a tow truck. If you have a tester at hand, you can check it yourself at home.

A multimeter is a universal device. It is used to measure leakage current and battery voltage. We set the regulator knob to 20 Volts DC voltage and measure the health of the battery. Red probe for the positive terminal, black probe for the negative terminal. The readings should be from 12 volts when the car is not started and up to 14.7 volts while the engine is running. Depends on the brand of the car, and accordingly on the generator and the general layout of the installed equipment. The charge level is checked an hour after stopping the engine.

Checking the battery on a car using a load fork

The load fork is a unique device for measuring the charge, voltage, and load of a car battery. Consists of: voltmeter, spiral, probes.

Load plug for battery testing

It has a simple design and low price. Can be purchased at any automotive store. Let's look at how to use the load fork:

Measurement without load. Connect the black alligator clip to the negative terminal. Angular contact with the inscription “B” to the positive one. Measure the voltage.
Measurement under load. Disconnect the battery from the vehicle completely. Touch the plus with contact “H”. Take the measurement for 5 seconds, but no more.

Below is a table of plug readings when checking the battery:

Table of percentage of charge versus voltage

The table shows that the value under load. Diagram for checking battery capacity

There are special battery capacity testers. The test is done using probing pulses processed by a microprocessor. Next, based on the data received, the tester determines the battery capacity. One such device is SKAT-T-AUTO. Takes a measurement within 15 seconds. Fully automatic.

Thus, having measured the readings, we compare them with the nominal value indicated in the passport or on the battery itself; if the value is about 50%, replace the battery.

SKAT-T-AUTO

Checking the electrolyte density in the battery

The density in a battery depends on the concentration of sulfuric acid in the electrolyte. Measured in g/cm3. The concentration of sulfuric acid depends on the degree of charge, temperature, and the presence of defects in the jars. When the battery is discharged, part of the solution penetrates the plates and the density decreases.

The test can be carried out at home at a temperature of 25 ° C and a fully charged battery. The electrolyte density should be 1.28±0.01 g/cm3. The dependence of density on voltage, charge and temperature is presented in the table below.

Electrolyte density at different temperatures

Before checking the density, you need to look at the electrolyte level in the battery. It should be 15 mm higher than the separators.

Method for checking electrolyte level

To measure the density of the electrolyte in the battery, a special device is used - a hydrometer. The verification process consists of several stages:

Unscrew all the lids from the jars.
Squeeze the hydrometer bulb.
We lower the battery into the jar and collect the electrolyte.
The float on the scale will indicate the density of the electrolyte.

The density value in all battery banks should be the same. If the total value is lower, then this indicates low charge. With different densities in jars below 0.10 g/cm3, we can talk about a short circuit in one of the plates.

Hydrometer readings

How to check the battery for short circuits

The previous check will tell us this. If the density value in one of the cans is below 1.24 g/cm3 by 0.10-0.15 g/cm3, then we can talk about a short circuit. Next, you need to turn on the load by unscrewing all the caps. And look at the boiling point of the electrolyte on this jar. If it bubbles, it means the plates are closed. This check gives a 100% guarantee.

If the battery is running low

There are times when a car is parked and the battery dies overnight. First you need to check the battery itself with a load fork. If it is ok check the leakage current as follows:

We switch the tester to DC measurement mode.
We set the range to 10 A.
Turn off the ignition and remove the key from the lock.
Disconnect the negative or positive terminal of the battery, whichever is convenient. We place the device's pliers in the gap. That is, one probe is on the terminal of the battery itself, and the second is on the wire from the car.
On the device we will see the leakage current consumed by the car and its systems at the moment.

Tester connection diagram

It must be borne in mind that many modern cars have a power supply system that falls asleep 10-15 minutes after the ignition is turned off. Therefore, you have to wait until the electronics fall asleep. The normal value for leakage current is about 0.01 - 0.08 A. If the value exceeds, you need to look for the reason for the high consumption.

Do not connect the multimeter in current measurement mode to the plus and minus of the battery at the same time, the fuse or the board itself may burn out inside.

In order to find equipment that consumes increased current, it must be excluded from the general circuit of the car. We find the mounting block and one by one disconnect the fuses and relays from the consumers. As soon as the leakage current has decreased, we look at which fuse was removed and what it is responsible for. If this check does not help, disconnect the plus from the starter and generator.

Ways to check a car battery at home

The starter current source is one of the main elements of a modern car. It not only allows you to start the engine, but also supplies electricity to many important and useful propulsion and safety systems. A sudden battery failure can become a serious challenge on the road. In order to check the battery on a car, there are several simple ways.

Signs and causes of battery failure

An experienced driver will quickly guess about problems with the power source. To do this, he only needs a few signs, including:

Sluggish engine cranking, indicating a low charge level. His efforts are not enough to ignite the fuel mixture.
The battery drains quickly. Usually this problem is detected in the cold season, when a seemingly full battery goes out after a couple of cranks.
Energy consumers are unstable.

All these factors should not be ignored, since the final failure of the battery can occur at the most unexpected moment. To avoid consequences, it is necessary to diagnose the unit.

There are several reasons for the battery to malfunction. Among the main ones the following are considered:

The absent-mindedness of the owner, when electrical appliances are left on when leaving the car, which leads to the rapid landing of the container.
Low quality of equipment maintenance.
Increasing service life beyond established standards.
Technical problems in the electrical wiring system, which can result in oxidation and destruction of contact connections.
Incorrect connection of consumers leads to increased electricity consumption and reduced battery life.
The generator does not work well, disrupting the battery recharging cycle while driving.

The root causes of battery failure can be diagnosed and prevented. It is important that this be done by properly qualified specialists and using high-quality and reliable tools.

Using a Multimeter to Test

This device is in demand not only among motorists. It is used in any area related to electrical measurements, including using it to check the performance of the battery. The versatility of such a tool is explained by the fact that it combines a voltmeter, an ohmmeter, and an ammeter. The compact device does not take up much space in the car and is always ready to take the necessary measurements. The battery reserve lasts for a long time, if you remember to turn it off during a break in work.

When choosing an assistant to repair car electrical wiring at home, you need to take into account the following characteristics:

DC voltage is measured in the range from 0 to 200 mV, 2 V, 20 V, 200 V, 1 thousand V, and alternating voltage is measured from 0 to 200 V, 750 V.
Resistance testing parameters range from 0 to 200 ohms.
The DC current run-up in most models is 2, 20, 200 mA.

These basic parameters can be supplemented with different values and functions depending on the device model.

Battery voltage measurement

This is the most important parameter of the battery’s suitability for operation. Many drivers test this indicator first. This is done with the engine running. If the device scale displays values from 13.5 to 14 V, then everything is in order with this characteristic. Increased numbers will indicate a low charge level and more energy being supplied from the generator to maintain operating mode. This case often occurs in winter, when a faulty battery runs out of power.

There is no need to worry about short-term exceeding the standard data. In a technically sound car, the level stabilizes within 10 minutes. If during the specified period the indicators have not been restored, you need to pay attention to the serviceability of the voltage regulator or the condition of its contacts. If they become oxidized, they need to be cleaned. If there is a decrease in potential below 13 volts, you should think about replacing the battery, as this is an indicator of a faulty element.

If you take measurements with the car not running, you should pay attention to the following nuances:

A voltage lower than 12 volts will not allow the engine to start, especially in cold weather with thickened oil. The crankshaft will not turn due to insufficient force in such a situation. A normal level is considered to be no weaker than 13 V.
All measurements should be taken before the start of the movement, and not immediately after its completion.
A larger charge will keep the battery operating for a longer period. At a lower level, it will sit down faster. Therefore, a new battery or one in close to this condition remains operational longer.

Battery charge and capacity

To check a car battery using this method, you need to analyze the data from a multimeter. Measurements should be taken 5 hours after recharging or disconnecting the battery from the machine. The data in this case will be more accurate. They do not depend on the ambient temperature.

Considering such measurements, the following patterns should be noted:

A potential difference of 12.8 V indicates a fully charged battery. A large excess hints at serious malfunctions.
The 75% balance is indicated by the figure 12.6 V.
The marking 12.2 is taken as half.
12 volts will indicate a quarter of the resource.
Anything less than the last value indicates a minimum reserve.

Information about capacity is no less important than charge. You can test it in the following way:

The battery must be fully ready for use.
Apply load to the battery. You can connect several lighting fixtures in series.
A weak glow at a voltage of 12.4 volts guarantees problems with starting the engine in winter.
Reducing the data below 12 V requires replacing the battery.

Such a check of the car battery provides an opportunity to avoid problems during start and movement, as well as prolong the operation of the product.

In addition, you can test the capacity by checking the control charge:

The battery must be completely full.
Turn it on at deep load according to the passport.
Connect the device to the circuit.
Measure the time it takes for the current to decrease by half.
If it matches what the manufacturer stated, then the battery is working.

Leakage current measurement

For any car, even a completely new one, this is an inevitable phenomenon. This is explained by the minimal electricity consumption of some consumers even when the engine is turned off. In reference books you can find numbers from 10 to 80 mA depending on the device. If this data is greater, then we can talk about a malfunction of the machine. The ideal value is 60 mA. The lack of daily recharging due to interruptions in operation has a more negative impact on the condition of the equipment.

Before you begin obtaining information, you need to prepare the vehicle for testing:

Disconnect the interior lighting, radio and other consumers.
Remove the keys from the ignition.
Check the information received. Exceeding values of more than 60 mA gives rise to a search for the circuit that receives the maximum power consumption. This can be done by elimination, removing fuse blocks one by one.

This preliminary procedure will provide more accurate information about both the condition of the battery and the power supply circuits.

The procedure for checking leaks is as follows:

Set the measuring range to 10 A or 20 A.
Disconnect the minus battery.
Connect the probe of the device to this place.
Connect the second one to the removed wire.
The result will be shown by an indicator board or arrow.

Other ways to test the battery

To check your car battery, you can use several more methods. Some of them will do without special equipment, others will require knowledge of electrical engineering. However, all of them are quite easy to produce even by not very experienced motorists.

Visual inspection

When purchasing a battery, it undergoes a thorough examination to determine the integrity of the case or the condition of the terminal connections. But such a procedure is simply necessary every time you open the hood of the engine compartment. This won’t take much time, but it can protect you from unpleasant incidents that can happen due to random little things. Once you lift the lid, you need to focus on the following questions:

Presence of cracks and leaks in the shell.
No contamination. This speeds up the self-discharge of the battery. A weak alkaline solution of 5 g of soda per 100 g of water is suitable for wiping.
Clean connecting pins from light green oxide. Sanding should be done using fine-grain sandpaper.
Tight connection of contacts. This will prevent heating and burnout of the wires.

Load Fork Testing

Using such a device, an analogy is created for the power consumed by the battery during startup. It includes terminal blocks, a voltmeter and a resistance. The whole action is divided into 2 stages:

Initially, measurements are made with the battery disconnected 7 hours after stopping the engine. If the electrolyte level is low, it needs to be added. The optimal air temperature is + 20 degrees. The filler plugs should be opened. The positive terminal must be connected to the positive pole of the battery, touching the negative electrode with the negative terminal. The readings on the display will reflect the charge level: 12.6−12.9 V corresponds to 100% filling, 12.3−12.6−75%, 12.1−12.3 V indicate half readiness; 11.8−12.7 V - a quarter of normal; Anything below the specified values indicates that the battery is low.
In operation, measurements are carried out on a charged battery. A load resistor should be connected to the plug and the circuit assembled, as when checking with the equipment turned off. It should be noted that sparks may appear on the contacts due to the high current flowing through them. The readings are recorded 5 s after switching on. The degree of charge is determined as follows: one hundred percent power corresponds to a voltage of 10.2 V, 75% is 9.6 V, 50% is 9 V, 25% is 8.4 V, less than 7.8 V is zero charge.

Study of electrolyte level and density

This operation is only possible on those batteries whose design allows for their maintenance. During the test, the battery should be positioned strictly horizontally with the caps removed from the cans. The liquid level is determined visually: the plates should be immersed by about 1 cm. A glass probe will help to more accurately determine the filling, which should show the filling of each jar by 10-15 mm. The electrolyte level should be increased by adding distilled water, after which the power source can be charged.

Density can be determined using an acid hydrometer, which is similar to a bulb with a glass bulb and a graduated float. The measurement is carried out on a fully charged battery at a temperature of 25 degrees Celsius. During work, the use of protective equipment is required: glasses and acid-resistant gloves.

To start checking, you need to lower the tip of the device into any jar and use a bulb to draw in a little liquid so that the indicator floats freely in it. Using a special table, you need to check the compliance of the scale readings to determine the suitability of the contents for subsequent use. Under normal conditions, a good electrolyte will reveal a density of 1.28 ± 0.01 g/cm3, and its decrease for every 0.01 g/cm3 means a 5-6% discharge. This procedure should be carried out once every six months.

Maintaining Battery Health

In order to extend the life of the battery and avoid troubles during startup or on a long journey, you need to follow a few simple recommendations. They are as follows:

Regularly clean the battery, tighten the terminal connections, and lubricate them with a special compound.
Once every three months, and more often in winter, charge it from a stationary device.
Do not allow the electrolyte level to fall below the maximum level.
Monitor the health of the vehicle's on-board power supply.

This will allow you to avoid unexpected expenses for purchasing a new power source and not be left in the middle of the road with a stalled car.

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.

How to check a car battery?

Checking the battery charge level takes little time and does not require high qualifications or expensive equipment. The operation allows you to check the condition of the battery and the need for charging. This is the first thing to do if you have problems with the starter. Also, the ability to check the charge will be useful when buying a new battery or servicing an old battery. In this article we will look at three ways to diagnose a battery: using a multimeter, an indicator and a load plug.

In this article you will learn:

Why check the battery charge?
Ways to check the car battery for performance
Video instruction

Also at the end of the article you can watch an instructive video that gives useful tips for quickly and accurately checking the performance of the battery.

Why check the car battery charge?

Lead-acid batteries, which are used in cars with internal combustion engines, have low internal resistance. This allows them to deliver the hundreds of amperes of current required to operate the starter. However, this type of battery cannot be subjected to deep discharge. Otherwise, the plates become covered with a layer of lead sulfate and the battery suddenly loses capacity.

A fully charged battery produces a voltage above 12.6 V. As the charge level drops, this figure decreases:

Given the tendency to sulfate, it is undesirable to discharge lead-acid batteries to less than half the charge. Therefore, if the voltage at the terminals drops to 12 volts, you need to immediately charge the battery.

When purchasing a new device, you should not buy severely discharged batteries. It is possible that sulfation of the plates has already begun in them. Therefore, if there is no indicator on the battery, it is worth checking it with a multimeter or a load plug.

How to check the battery charge using the indicator?

Many maintenance-free batteries have charge indicators that allow you to visually determine the condition of the battery. This option first appeared on Japanese products and quickly gained popularity due to its convenience and accessibility.

The hydrometer, as the indicator is called, is a transparent window on the battery cover. The color of the window changes depending on the condition of the battery:

Green —full charge.
Gray or white - need to be charged.

For some indicators, the window turns red when capacity is lost.

The principle of operation of the device is based on changes in the density of the electrolyte at different charge levels. It works like this:

A tube with a green float is attached to the window.

When charging the battery, the density of the electrolyte increases and the float rises, approaching the window.
If the battery is discharged, the density drops and the ball sinks in the electrolyte. As a result, the indicator window changes color to gray or black.

Some indicator models have a red ball that floats up when the density of the electrolyte decreases. This provides a red indication of the discharge.

When the electrolyte level drops, not the ball, but the electrolyte itself will be visible through the window. To prevent the destruction of the plates, you need to add distilled water to the jars and charge the battery.

The advantage of the indicator is that the device allows you to determine the condition of the battery without the use of special instruments. This is convenient when purchasing a battery or in road conditions when you need to quickly check the condition of the battery. However, indication using a float does not always allow one to draw accurate conclusions about the performance of the battery. Therefore, when in doubt, you should use a multimeter or a load fork. They are also useful when you need to check a battery that is not equipped with an indicator.

How to check battery charge with a multimeter?

To check the voltage at the battery terminals you need a voltmeter. However, instead of these specialized devices, it is easier to use universal measuring devices - multimeters. In addition to voltage, they measure current and resistance. Depending on the indication method, these devices are divided into two categories - digital and pointer . If you have a choice, it is better to buy a digital multimeter. It is simpler and more convenient to use.

On-board computers of modern cars are also equipped with voltmeters that display the voltage at the battery terminals. However, they are not connected directly to the terminals. Therefore, due to contact and wiring resistance, the on-board computer readings may differ from the battery voltage. With the engine running, the voltmeter on the dashboard shows too much voltage. If the engine is turned off, the device will give low readings.

Readings must be taken with the engine running and switched off. In the first case, you will be able to check the condition of the battery and wiring, in the second - only the battery.

Measurements while the engine is running

Place the car on a level surface, open the hood, put the handbrake on and start it. When the engine is running, the generator and voltage regulator operate, which charge the battery. Therefore, the voltage at the terminals should be within 13.5-14 volts. In some cars, when the battery is discharged and the air temperature is low, the electronics automatically increases the voltage to speed up charging. In this case, it should fall smoothly as it charges. If this does not happen, the electrolysis process is activated in the banks. The electrolyte will begin to boil away rapidly. Overcharging is especially dangerous for modern gel batteries with limited gas emissions.

A voltage of less than 13.4 volts is a sign of undercharging. Operating in such conditions promotes sulfation of the plates and shortens battery life.

When measuring voltage, you need to turn off all powerful consumers: headlights, heater, audio system. Otherwise, the power of the generator when idling will not be enough to maintain the optimal voltage level.

There are several possible reasons for low voltage at the terminals:

Poor contact.
Generator failure.
Voltage regulator malfunction.

You cannot operate a machine whose battery is in undercharge mode. The cause of the failure must be immediately localized and eliminated. If the voltage at the terminals and the output of the generator is very different, you need to clean the contacts on the battery with sandpaper or a file.

After checking without load, you need to turn on the headlights and other powerful energy consumers, add engine speed and repeat the measurements. If at high speeds under load the voltage drops to 13.4 volts or lower, diagnostics of the generator system and control unit is required.