Why Do Full EVs Still Have a 12v Battery?

Sep 11, 2023

If your EV has a massive battery, why does it also need a regular 12v battery?

Your electric vehicle comes with a massive battery; not only can it help you travel miles, but it also enables you to reach speeds of 60 miles an hour in less than six seconds (and even faster in a Tesla Model S Plaid, which demolishes it less than two seconds!).

But did you know that your EV still has a regular 12v battery, just like any other regular vehicle? But if your EV already has a massive battery, why does it also need a 12v battery?

Before getting into 12-volt batteries and why they are needed on an electric vehicle, it's essential to understand the electrical systems of an EV.

Your EV has two distinct electrical sub-systems, each designed to deliver different amounts of power to the electronic parts that move your electric vehicle.

As explained earlier, your electric vehicle comes with two electric systems; one that moves it and requires high voltage and another which provides all the user comforts and safety and runs on lower voltages. To power these two distinct sub-systems, two different batteries are required—a high voltage battery with a range of 400-800v and another 12-14v low voltage battery.

Therefore, the 12v battery on your vehicle is responsible for powering the low-voltage electronics, as using a high-voltage lithium-ion battery to power these parts would fry them instantly.

But can't the voltage of a lithium-ion battery be stepped down using a DC-DC converter and be used to power all the low-power systems? After all, this would remove the clunky 12v battery from the car, making it lighter.

There are several reasons why the 12v battery on your EV can't be replaced.

Looking at all the points given above, it makes sense to have the clunky old 12v battery on an EV. That said, what happens when the battery on your vehicle fails?

Without the small 12v battery, your electric vehicle would be bricked—so don't throw those jumper cables you have lying around.

As explained earlier, the high-voltage battery drives the propulsion system, but to connect all this power to the motor, the 12v battery needs to energize a contactor that connects both systems. So, if you look at it, if the 12v battery on your electric vehicle gives up, you won't be able to start it without bringing the 12v battery to life.

Unlike a vehicle powered by an ICE, an electric vehicle does not have an alternator. This raises the question of how the 12v battery on an EV is charged.

Well, the lithium-ion battery charges the 12v battery using DC-DC converters. These DC-DC converters are devices that convert the high voltage from a lithium-ion battery to a lower voltage in the range of 14-16v using simple electronic parts such as a capacitor, inductor, and transistor. This voltage is then used to charge the battery while the electric vehicle runs.

Just like conventional vehicles, most electric vehicles also use lead-acid batteries. That said, this trend is changing, and the new Tesla Model S and X come with lithium-ion auxiliary batteries. This change in battery technology for electric vehicles is due to two reasons.

Electric vehicles have changed how we commute; that said, 12v batteries play a crucial role in how an EV works. Therefore, an EV will always have an auxiliary battery system, but the voltage or battery technology for these batteries could change in the future.

Nischay is an Electronics and Communication engineering graduate with a knack for simplifying everyday technology. He has been making tech easy to understand since 2020, working with publications like Candid.Technology, Technobyte, Digibaum, and Inkxpert.In addition, Nischay loves automotive technology and has been working as an Engineer with Stellantis for the last two years. He has adept knowledge about the features that makes today's cars safer and easier to drive.