Testing a car battery: This is how easy it is to recognize an empty battery

An empty car battery is not the end of the world, but it is enormously annoying – because if the car doesn't start, you usually have trouble. To prevent this from happening in the first place, you can test the car battery. We tell you how the car battery voltage is measured and what you need for it.

 

What are the first signs of a low car battery

Most problems with a weakening car battery are in winter, when you let the car warm up or the windows are frozen inside, the battery has to do a lot, because the car does not move at first.

There are two typical signs of a low battery. The car does not start immediately after starting. The motor rotates a little longer and you can really hear how the battery has to exert itself. The second sign is that electrical consumers such as the air conditioning or the car radio initially have dropouts after a cold start.

As long as there is still a minimum voltage, it will settle down again after a few minutes of driving, because the battery is charged while driving. But that doesn't solve your problems, because the car battery is and remains weak. Therefore, a car battery test is now definitely necessary.

Especially if you often drive short distances, it is good to test the car battery at regular intervals, because the battery terminals get dirty faster and a defect can occur sooner - if you don't take care of the battery. It is also possible that the steering wheel lock can no longer be released if the battery is too low.

 

Check car battery without measuring devices

If you're not that tech-savvy and you're already sweating just thinking about having to do a car battery test, we can reassure you. You can also check the condition without a tester for the car battery – this is also called a multimeter.

It has to be dark outside and you need a wall. Stop in front of the wall and turn off the engine, but turn on the low beam. If the light gets darker shortly after switching on – which you would see on the wall in front of you – the car battery is already quite low.

 

Measuring the voltage of the car battery with the multimeter

Measuring the condition of the car battery with the multimeter will certainly provide more accurate results. But make sure that the car has been parked for a few hours before the test, because shortly after a drive you falsify the results. To test, you get the aforementioned multimeter and can then check the condition of the car battery. This is how it works:

• The red cable of the multimeter is connected to the positive terminal of the battery.
• Connect the black cable to the negative terminal.
• The multimeter will now show you the voltage – it should be between 12.4 and 12.7 volts at best.
• At 12.7 volts, the state of charge would be 100 percent, at 12.4 volts 70 percent.
• Below 12 volts, there is a defect in the battery.

You can first try charging your low battery overnight and then test it again the following day. If the result is the same, you will need to replace the battery.

 

What does the car battery voltage say about the state of charge?

Now that you already know the multimeter, let's also tell you what the respective state of charge is at the different charging voltages that you can measure:

Battery charge level (in percentage)	Voltage for normal battery (in volts)	Voltage for battery in cars with start-stop function (in volts)
100	12,70	12,90
90	12,60	12,75
80	12,50	12,65
70	12,40	12,50
60	12,30	12,40
50	12,20	12,25
20	11,80	11,80
0-10	10,50	10,50

 

Start-stop battery: What to consider with modern batteries

In the meantime, new car models are equipped with the so-called automatic start-stop system. This system also requires a different battery – and there are several things to look out for to test whether it should be used further.

SOC – State of Charge

SOC is the state of charge of the car battery. This is no different from any conventional battery. The state of charge can be measured just as easily with a multimeter, as described above.

SOH – State of Health

The second component when testing a start-stop battery is the SOH, the state of health, of the battery. Unfortunately, this is not so easy to test. To determine the state of health of the battery, the cold start capability (CCA), the remaining capacity (Ah) and the charge absorption (CA) must be tested, among other things.

Charging the car battery extends the life of the battery

As already mentioned, you should check your car battery regularly and pay attention to it. If the voltage is between 12.7 and 12.4 volts when fully charged, then everything is fine. If it is permanently below this or if the voltage drops significantly after a short time - perhaps even below 12 volts - then the battery is unfortunately broken.

If there are permanently low charge levels, sulfation occurs. This means that deposits form on the charging plates due to influences such as cold or moisture. Over time, the disks can no longer absorb a charge.

So if your battery is still in a good range, it is best to charge it completely again and again so that it does not come to a permanently low state of charge. This allows you to use the battery a little longer.

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