How to check if a car battery is charged

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Sergey Trofimov

Lutz Winkler

Sergey Trofimov

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 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.

Diagnostics of the battery with a multimeter with the engine turned off

In this state, the normal voltage on the battery is 12.5-13 volts. Lower readings on the device indicate a discharge.

How to check your car battery for performance

If during the operation of the car there are problems with starting the engine, the starter turns slowly or nothing happens at all after turning the key, check the charge level of the battery. There are several different ways to do this; we will consider each of them separately.

How to test a battery with a multimeter

The voltage at the battery terminals can be measured using an autotester. It is better to take measurements after parking overnight, before starting the engine. We set the multimeter to measure DC voltage (DCV - 20), and install the probes in the sockets (black - COM, red - in the positive polarity socket). We connect the probes of the device to the battery terminals and take readings (example in the video):

We compare the obtained values with the table:

It is worth noting that this method of checking the battery is ineffective. Despite this, the majority of car enthusiasts choose this method. To accurately determine the level of battery discharge, use one of the following methods.

How to check battery density

To check the electrolyte density, use a hydrometer or a commercially available electrolyte density float indicator. We collect electrolyte from the battery jar into a glass flask and lower the hydrometer. We determine the density using the scale and compare it with the table:

Depending on the battery model, the initial density of the electrolyte may differ (see the battery instructions). The process of determining the density of the battery electrolyte is shown in the video:

How to test a battery with a load fork

A load plug is a device that allows you to determine the battery voltage under a load of 150-200 A. We connect the load plug to the battery, observing the polarity. Apply the load by pressing the device. At 5-6 seconds we take readings from the device. The voltage must be more than 9 V, otherwise the battery is dead.

The process of checking two batteries using a load fork in the video:

How to check a battery without instruments

You can determine the performance of the battery without special instruments. For example, to test a 60 Amp/hour battery, you should create a load of 30 A. To do this, for example, you can connect 6 low beam lamps (55W) in parallel to the battery. If after 5 minutes the lamps begin to glow dimly, the battery is dead.

In conclusion, a couple of tips . If the battery charge level is 75% or lower, you must remove the battery from the vehicle and charge it using a charger. As practice shows, if the battery life exceeds 3 years, and problems begin with starting the engine at low temperatures, it is advisable to replace the battery with a new one. If the battery is draining quickly, there may be leakage current.

Let us remind you that we previously told you how to properly light a car with a dead battery. Have you ever checked your car battery yourself? Which method did you use?

How to test a car battery for performance at home without instruments

Hello, our dear readers! Since most of you are motorists, you have probably encountered issues with battery maintenance and repair. Therefore, the topic for discussion will be how to test a car battery for performance without having any special tools or devices.

Some will say that it is impossible to do this at home, and even without equipment. You will need to use a tester, multimeter or load fork.

Yes, all these devices are really good for checking and maintaining your battery. But there are several actions that you can perform at home with virtually your bare hands.

Some of the rules below must be followed when purchasing. But they will also help check the current condition of the battery and evaluate its performance.

Visual condition check

Here you should immediately understand that you will not be able to obtain any numbers and measurement results, as is the case with the use of testers and multimeters. But we don't need that.

In many ways, you can determine by the external condition of the battery whether it is good or bad, how long it will last and whether it can still perform its functions at all.

I recommend carrying out such procedures before purchasing a new battery, as well as when purchasing a used car.

Frame. No damage or defects are allowed. Otherwise, if the design is violated, the battery may cause a short circuit, fail at the most inopportune moment and simply not start the engine;
Dust and dirt. Their presence is not critical, but it is better when the battery remains clean. Keep an eye on this;
Terminals. It must also be clean. But here it is extremely important to see if there is a white or greenish coating on the terminals. If there is, this is a sign of oxidative processes. The battery is bad;
Moisture and traces of leaks. If electrolyte is leaking, it is not difficult to notice visually. Traces of moisture also indicate that the battery is gradually reaching its end;
Fastening and fit. Be sure to check how tightly the terminals are and how tightly the fasteners are tightened, holding the car battery in its rightful place in the engine compartment. If everything is based on snot, it's bad.

If moisture and dirt accumulate on the battery, this will cause accelerated self-discharge. When the terminals are not tight enough, the resistance at the connection areas increases. The starting current will decrease, making it more difficult for the starter to start the engine.

Overheating of the terminals also does not bode well for the car owner. Therefore, such a phenomenon cannot be allowed.

In order for the battery to work well and for a long time, it requires proper care. After all, there is absolutely nothing difficult in periodically removing all dirt and wiping the body with a dry cloth. You can shine a light bulb on yourself to study the condition of the equipment in more detail.

One more point regarding care when traces of electrolyte appear or plaque forms on the terminals. There is no need to throw away the battery. But if leaks are detected, the electrolyte must be properly removed. To do this, make a weak alkaline solution. It's easy to prepare. Take 100 milliliters of water and add a teaspoon of soda. Everything is thoroughly mixed and the surface is wiped with a sponge. Then wipe everything dry with rags.

When oxidizing the terminals, use fine-grained sandpaper. Disconnect the battery first. Next, it would be a good idea to treat the cleaned terminals with technical Vaseline. Or just take some oil from the dipstick and lubricate them. The oil also adequately protects against acidification.

Checking without devices and tools

Left without a multimeter and without a load plug, you can still check the performance of the battery. Even in the field.

There are a huge number of thematic videos on the Internet in which experienced and not so experienced motorists give useful tips on servicing batteries. But the problem is the same everywhere. Almost every such video begins with words like “take a tester” or “using a multimeter.” What should a person who doesn’t have them do? Moreover, the battery turned out to be maintenance-free. I'll say this. You can't give up. But there is something you can do. And even necessary.

Let's start with the fact that many modern cars are equipped from the factory and are equipped by the car owners themselves with so-called maintenance-free batteries. But this fact should not stop you from diagnosing it.

Manufacturers have provided in advance for the user (driver) to monitor such batteries and their performance. For this purpose, appropriate built-in indicators are provided, as well as systems for self-diagnosis.

To determine the condition of such batteries, you just need to look at the instruction manual. That's all.

And if you want to check the battery for serviceability, but you don’t have any special instruments, there is a great way. You need to do the following:

Look at the external condition of the battery. All those procedures that we talked about above;
If there are contaminants, get rid of them;
You also need to tighten all the terminals if they are loose and tighten the fasteners;
Do not start the engine;
At the same time, turn on all the lights that are available in the car;
Wait 5 minutes;
If the intensity of the glow has not changed, everything is fine with the battery.

You yourself can clearly see that there is nothing complicated in this procedure. And we didn’t need any special measuring instruments.

I don’t argue that these are conditional data, which cannot be used to fully assess the performance of the battery in a car. But sometimes such measures are enough. So at least you know that you can drive a car, and the headlights will not turn off in the middle of the night on the road.

The car itself usually lets you know that there are problems with the battery. At first the symptoms are barely noticeable, but gradually the situation only gets worse. If you see that the engine is difficult to start, there is a high probability that the battery is at fault. They are faulty or severely discharged.

The battery is an extremely important component of almost any vehicle. Therefore, monitoring its performance is the sacred duty of every motorist.

Do you know any non-standard methods for checking batteries without using different testers and special equipment? If yes, be sure to write about them in the comments. Let's discuss everything together.

That's all I have for today. I hope you found it interesting and even fun at times.

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Checking and charging the battery

The vehicle battery is subject to periodic inspection and must be kept clean and charged. Contaminated surfaces lead to increased self-discharge. The presence of oxide or dirt on the clamps significantly impairs starting the engine with the starter due to significant voltage losses in the connections. If the battery is often left for a long time without recharging or in a discharged state, this leads to sulfation of the plates, a decrease in capacity and an increase in the internal resistance of the battery.

When measuring the electrolyte level, unscrew the plugs from the caps and lower a measuring glass tube with a diameter of 3-5 mm one by one. It must be held vertically, lowered all the way into the safety shield, which is located above the plate block. Then close the end of the tube tightly with your thumb and remove the tube from the battery. The electrolyte level should be 10-15 mm; if it is less, then you need to add distilled water.

The density of the electrolyte is measured with a hydrometer. To do this, you need to squeeze the hydrometer bulb and insert it into the battery jar, release the bulb, remove the hydrometer and determine the density using the float scale. For our climate zone, the electrolyte density should be 1.25-1.27 g/cm3. If it does not correspond to this value, then it is necessary to charge the battery with a charging current equal to 0.1 C, where C is the battery capacity. For example, if you take a 6ST-75 battery, then the charging current should be 7.5 A. The battery must be charged for 10-12 hours, until the electrolyte boils.

The load fork is designed to check the serviceability of a battery with a capacity of 42-135 A/h. If the battery is in good condition and fully charged, then the voltage will not be lower than 10.2 V, and in each battery bank - 1.7-1.8 V. If the voltage is 1.4-1.7 V, then the battery is charged, and below 1.4 V - the battery is faulty (sulfitation of the plates) and needs to be repaired.

Checking and charging the battery.

To do this, remove the battery from the car and clean it from dust and dirt. Electrolyte that may be on the surface of the battery must be wiped with a cloth soaked in a 10% solution of baking soda. Using brushes, clean the battery lead pins and terminals and lubricate them with petroleum jelly or grease. Inspect the monoblock battery for cracks.

Check the electrolyte level by unscrewing the plugs and using a measuring tube
to check the level, and if necessary, add distilled water.

Using a hydrometer, check the density of the electrolyte in each jar and, if necessary, charge the battery.

Check the voltage using a load plug. To do this, you need to turn on the appropriate load resistor depending on the battery capacity and press the legs of the plug to the battery pins. At the end of the fifth second, the measured voltage of an individual bank should be at least 1.7 V, and the battery as a whole should be 10.2 V.

If the voltage and density do not meet normal values (Density 1.25-1.27 g/cm3, battery voltage 1.7-2 V, or 10.2-12 V for batteries), then charge this battery or battery with current I = 0.1 C, where C is the battery capacity.

Repeat the measurements, if they do not change, then the battery is unsuitable for use.