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Why does an electric car need a 12-volt battery?

The 12-volt battery in an electric car is used for the same purposes that traditional gasoline cars are using the 12-volt battery for. Your infotainment system, air-condition, lights, locks, and every other accessory on your car run on this 12-volt battery.

So actually your electric car has two batteries, you have the 12-volt lead-acid battery and the much bigger 200+ volt lithium-ion battery as the main one.

So why not just use the main battery for everything?

The 12-volt lead-acid battery has several functions. Running all accessories from this battery is balancing out higher loads on the system so that the main battery is for powering the motors only. Also, it functions as a fail-safe for other electronics like brakes and thing that has to stay “alive” even when the car is powered off.

The main battery is actually also fairly dangerous. This is because of its really high voltage compared to the smaller 12-volt battery. So when you turn off your car, there is a large relay (a contact/switch), which disconnects the main lithium-ion battery from everything else.

So to actually turn your electric car on, you really depend on this smaller 12-volt battery. If you don’t have that second battery you cannot initialize the various ECU’s and control units and switch the relay back again to connect the battery to the system.

As electric cars have a large main capacity, the 12-volt lead-acid batteries didn’t actually have to be as large as they are today. They do take up a lot of space compared to their function and the actual need for kilo-watts. But I think manufacturers have just kept the standard model as this is a part that would need to get changed over time. Also, it’s good to know that your electric car has a substantial reserve for lights, radio, etc. if you should forget that you left something on when leaving the car for the night.

Author: Morten Pradsgaard

Morten has been working with technology, IoT, and electronics for over a decade. His passion for technology is reflected in this blog to give you relevant and correct information.