Testing your car battery: How to do it
The most important information about testing and measuring the car battery at a glance
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Why test car battery: To avoid car breakdowns and extend the service life, it is important to check, measure and charge the car battery regularly, because this is part of battery care.
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Signs of a faulty battery: You should check your battery if the engine stutters when you start, the indicator lights are darker than usual, the heater is weaker, or the radio is dropping.
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What values you should measure: To get information about the condition of the car battery, voltage, state of health and acid density play an important role.
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Battery tester: There are several devices that can test a car battery. These include multimeters, voltmeters, voltage testers or battery testers, and an acid lifter.
Why you should check your battery in the car regularly
To ensure that you always reach your destination safely, comfortably and efficiently, a charged and functional battery is essential. Most car breakdowns in Germany are due to a poorly maintained or well-maintained battery. In order not to break down with your car, it is important to have the car battery tested regularly.
The metric that is most relevant for drivers is the state of charge of the starter battery. Modern vehicles usually have different light modes and a variety of consumers such as seat heating, alarm system, rear window heating and radio, which demand a lot from the starter battery.
Especially in the cold season, it is annoying when the battery weakens or runs out completely and you may have to wait a long time in the cold for the breakdown service after starting problems. It is not only winter that is critical for weak batteries. Frequent short-distance journeys, without the battery being recharged via the alternator on a long journey, can also weaken your battery performance. Long downtimes, during which self-discharge and leakage currents contribute to the sulfation of your car battery, reduce the capacity. In the process, crystals of sulphate are formed, which, in the worst case, can lead to a short circuit and thus to premature battery death after a deep discharge.
In our guide you will learn how you can effectively prevent a deep discharge of the car battery. By regularly testing your battery in the car and the corresponding trickle charges, you can significantly extend the life of your battery.
Permanently low charge level damages the battery
A fully functional car battery should have a voltage of around 12.8 volts – when fully charged. While a charging voltage between 12.4 and 12.8 volts is still considered sufficient, it could be a sign that the battery is weakening if it does not reach these values at all or if the voltage drops below 12 volts again after a short time. If the charge level of the car battery is permanently low, this can lead to damage to the battery due to sulfation.
Due to various influences such as moisture or cold, the charging plates of the battery can sulphate, which means that they can no longer accept a charge. In this case, you should immediately replace the starter battery with a new one.
Check your car battery more often if you make frequent short trips
Drivers who regularly drive only short distances and do not continuously test and charge their car battery may be surprised by a defect in the starter battery even earlier. On average, the lifespan of a well-maintained battery is around 5 years. With good maintenance and regular recharging, a battery can last 6 to 8 years or more. Wear and tear on the battery terminals, on the other hand, can shorten the life of the car battery. If the battery terminals are dirty, e.g. due to leaves or oil residues, leakage currents can occur, which results in a faster discharge of the starter battery. Even in idle mode, more current flows than usual, the voltage decreases and the life of the battery is coming to an end.
Caring for a car battery means measuring and charging
You can do something good for your battery by driving longer distances at a time or charging the battery regularly using a charger. This is particularly important in winter, because in the cold season the charge balance of the battery decreases due to many electrical consumers such as seat heating, heated exterior mirrors or rear window heating. In addition, the battery absorbs less charge in sub-zero temperatures and charging can take correspondingly longer. When charging with the charger, however, you cannot see the condition of the battery, because other values play a role.
Are you unsure about battery technology, don't have enough experience to tell if your car battery is in good or bad condition? Then use the battery check from HUK-Autoservice in a car workshop near you. Our professionals are just a few clicks away.
Battery replacement with HUK car service: How it works
What are the signs of a weakening starter battery?
You should already know the first signs of a flat car battery to prevent an avoidable breakdown. If the engine stutters when starting, the indicator lights on the dashboard shine darker than usual, the heating warms up more slowly or the radio has small dropouts shortly after starting, you should urgently measure the vital signs of your battery.
Car battery – what and which values you should measure
Before each battery test using a measuring method, a thorough visual inspection of your battery for external damage should be carried out for your own safety. Pay attention to the leakage of acid, the secure attachment of the battery and the cleanliness of the connections. Cleanliness prevents leakage currents and thus self-discharge. The shelf life of your battery is extended. After the visual inspection, you can measure various functions of your electricity storage system.
Charge level of a battery
The most frequently queried metric to determine the state of charge of a battery is the voltage in volts. It gives you a statement about the state of charge (SOC) of your car battery and whether it's time to perform a trickle charge. Values between 12.4 and 12.8 volts are considered normal. If the battery no longer reaches these values at all or if the voltage drops below 12 volts again after a short time, the battery is no longer functional.
The statement of whether a battery is "full" or "empty" is crucial for all vehicles. For cars that use an automatic start-stop system, in which the battery is exposed to greater stress, the "state of health" should also be determined regularly.
State of health of a battery
The state of health of a car battery is a measure that indicates the degree of deterioration and the remaining capacity of the battery. It describes the difference between the condition of a new starter battery and the condition of a used battery. The determination of the state of health of a battery (SOH) is mainly carried out in the case of start-stop batteries such as an EFB or AGM battery.
With the more complex test procedure, a more reliable statement can be made about the condition of the battery in the case of the more heavily stressed start-stop batteries. In addition to the state of charge in volts (V), the cold-start power in amperes (A), the remaining capacity in ampere-hours (Ah) and the charge absorption (CA) also play a role here. These additional sizes for start-stop car batteries cannot necessarily be reliably tested – at least not with the common battery testers. If you are using an EFB or AGM battery, please contact a competent car workshop regularly to have a health check carried out on your battery.
Our tip: With the more than 450 partner workshops of HUK-COBURG, you and your car are in the best hands for a professional battery check. Whether starter or supply battery, lead or lithium-ion battery, with or without start/stop system: Our professionals test, charge and change every car battery on any vehicle from as little as 115.99 euros.
What voltage indicates which state of charge of the car battery?
In order to find out which voltage of the car battery gives which conclusion about the state of charge, the quiescent voltage of the battery is crucial: The voltage measured in the idle state of your acid or EFB battery should normally be somewhere between 12.4 and 12.7 volts. If the charging voltage is one value below, you should charge the car battery after testing to ensure that it continues to function reliably.
The following table will help you determine the approximate state of charge of the car battery based on the measured charging voltage:
| Quiescent voltage in volts (normal starter battery) | Quiescent voltage in volts (AGM battery with start-stop function) | Charge level in percent |
|---|---|---|
| 12,7 | 12,9 | 100 |
| 12,6 | 12,75 | 90 |
| 12,5 | 12,65 | 80 |
| 12,4 | 12,5 | 70 |
| 12,3 | 12,4 | 60 |
| 12,2 | 12,25 | 50 |
| 11,8 | 11,8 | 20 |
| 10,5 | 10,5 | 0-10 |
Testing a car battery: How does it work?
To check the most important value of your car battery, the charge level in volts, you can use a voltmeter, multimeter, voltage tester (voltage meter) or battery tester. The terms are often used synonymously. Basically, the procedure is very similar. If in doubt, you should always read the instructions for your device anyway. There are many manufacturers on the market.
In addition to the classic battery testers with so-called alligator clips, which you attach directly to the battery terminals, there are now testers for the cigarette lighter. With these you don't even have to open the hood, you just put them in the cigarette lighter. Some models remain plugged in permanently, measuring and transmitting the charge level of the car battery in voltage (volts) via app. This can be especially useful if you don't use the car often, but want to know before use whether it starts reliably. In addition, you do not need any experience in handling measuring instruments. As good as that sounds, you should definitely pay attention to quality with such models, as they are controversial when it comes to the significance of the measured values.
Nowadays, many battery testers are also combination devices with an integrated charger for batteries. If the battery voltage indicates that your battery is already alarmingly discharged, you can directly initiate a charge until functionality is restored by charging via the alternator or battery charger.
On the one hand, we will show you how you can test your car battery yourself with a simple process and on the other hand, we will show you the most common methods to test a 12-volt car battery with and without a multimeter.
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