How do I know if my car battery is failing?

A car battery that is starting to fail can cause starting problems and various electrical issues.

Common signs of a weak battery include:

• The starter motor turns more slowly than usual.

• The car is difficult to start, especially in cold weather.

• The battery needs charging frequently.

• Electrical equipment performs poorly when the engine is off.

• The car displays low battery voltage warnings.

• The battery loses charge even though the car is used regularly.
  

How do I check the battery’s condition?

You can start by measuring the battery’s resting voltage with a multimeter.

For a standard 12 V lead-acid battery at around room temperature, the following values can be used as a rough guide after the battery has been allowed to rest:

Resting voltage	Approximate charge level
12.7–12.8 V	Fully charged
12.5 V	Approximately 75%
12.2 V	Approximately 50%
12.0 V	Approximately 25%
Below 12.0 V	Heavily discharged

The values are approximate and do not apply to all battery technologies.

Important: Voltage mainly indicates the battery’s charge level, not its health.

A battery may show a normal resting voltage but still struggle to deliver sufficient starting current.

For a more reliable assessment, the battery needs to be tested with a suitable battery tester.

If the battery repeatedly discharges, the car’s charging system and any abnormal current consumption should also be checked.