Why do electric cars actually need a 12-volt battery?

22. Jan 2023 | Industry + More

A look at the breakdown statistics of the ADAC reveals a - supposed - surprise. For example, the figures from 2021: Here, the most common breakdown cause for electric cars was the 12-volt starter battery, just like with the combustion engine. A delicate 12-volt energy storage system in electric vehicles with 400 or 800 V vehicle electrical system is responsible for almost one in every two breakdowns. But why do electric cars actually need a 12-volt battery?

In addition to the high-voltage battery that supplies the power for the electric motors,electric vehicles usually also have a 12-volt battery installed. The high-voltage battery actually "only" supplies the drive and the interior heating with power for the most part. The rest of the consumers run on the 12-volt vehicle electrical system.

The 12-volt battery also starts the engine in an electric car

With electric motors too, one task of the 12-volt starter battery is to start the vehicle. The battery management system, which is responsible for almost all the monitoring and control tasks of the drive battery, is also supplied by the 12-volt battery. So the battery management system wouldn't even start without the small starter battery. And if the 12V battery fails, the drive battery cannot be charged either.

Buffer to create redundancy for important safety systems

The question still remains of why the energy for starting the electric motor cannot be taken directly from the high-voltage battery via a voltage transformer. "In fact, a system without a 12-volt battery is conceivable", explains Jochen Kramer, project manager for the electrics of the Porsche Taycan, talking to auto, sport. The problem is that the 12-volt battery also acts as a second power source to ensure uninterruptible function of safety-critical systems if the large battery fails. For example, systems such as ABS or ESP. The 12-volt battery therefore acts as a buffer to create redundancy for important safety systems.

In summary: The 12-volt battery is not just a safety or comfort issue. If the 12-volt battery in an electric vehicle fails, nothing works at all. Drivers of electric cars should therefore also pay attention to the small battery and have it checked regularly by their workshop.