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Why do electric cars have a 12v battery?

12-volt batteries power the low voltage systems in your electric car that always require power, like the ECU, locking system and 4G modem


Electric cars use 12 volt lithium batteries for low voltage accessories because it is simpler, cheaper and safer than using the 400v or 800v main battery


While lead-acid 12v batteries are the most common type, Tesla now uses a lithium-ion 12v battery and other car makers will probably follow suit


Logic dictates that an electric car with a huge lithium-ion battery shouldn’t need a 12v battery, yet most electric cars have one.


You might also notice that while your EV has a state-of-the-art lithium-ion battery, the 12v battery is an old lead-acid type.


Why? Because like internal combustion engine cars, electric cars have electrical systems that need to run all the time. A 12v battery is the most efficient way to power them because they require a very low voltage.


You could run all 12v systems off the main battery pack, but this would require a voltage conversion and add unnecessary complexity to the battery management system. It is safer and cheaper to just use a 12v battery!


Why do electric cars have a 12v battery?

There are three reasons why electric cars have a 12v battery:


Cost. 12v lead-acid batteries are dirt cheap, and there are hundreds of electrical systems in electric cars that run on 12v power. It is cheaper to use a 12v battery than it is to engineer a battery management system that creates a DC-DC conversion from 400v (the voltage that most electric cars run on) to 12v.


Simplicity. Lead-acid 12v batteries have been used for over fifty years, offering proven durability and a relatively long lifespan. Designing an electric car to run low-voltage systems with a 12v battery simplifies engineering.


Safety. Would you want your keyless door handle to be powered by a 400v or 800v system? 12v is significantly safer and more efficient. By disconnecting the main battery back from critical systems, the higher voltage is isolated.


How is the 12v battery in an electric car charged?

A 12v battery can be charged by the electric motor in drive, although in most electric cars, it is topped up by the main battery directly via a converter that steps down the voltage from 400v/800v to around 14v.


It is more efficient and economical to run the ECU, central locking, alarm, 4G modem and other critical and accessory systems off 12v and have the main battery or electric motor top up the 12v battery in drive or when plugged in.


You can’t charge a 12v battery with an 11kW charger, or any other charger, because it is charged by the electric vehicle itself.


What does the 12v battery do in an electric car?

12v batteries power electrical systems and accessories that run on a low voltage, like alarms, lights and central locking. Systems that run on a low voltage have their own battery to simplify the battery management system.


The 12v battery also powers the car’s ECU (engine control unit), the brain of the car, and the electric motor on start-up. So, without a 12v battery, you can’t drive!

Tina Yu

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