Did you know all EVs have a traditional 12-volt battery, and without it they won't start? Learn more about this surprising EV feature.
What To Know About the Electric Vehicle 12-Volt Battery
Updated on Aug. 20, 2024
Most people don’t realize an electric vehicle (EV) needs, or even has, a conventional 12-volt battery. They’re rarely talked about, but they should be! An EV’s 12-volt battery is just as essential as its high-voltage battery.
When speaking to technicians about EV 12-volt batteries, I’ve heard essentially the same thing: There are similarities and differences between an EV’s 12-volt system and an internal combustion engine (ICE) vehicle’s conventional 12-volt system. But an EV’s 12-volt battery also has its own set of unique functions and issues.
Twelve-volt batteries were introduced in cars and trucks during the mid-1950s. Affordable and dependable, they protect and stabilize the entire low-voltage electrical system on EV and ICE vehicles. If you’re considering purchasing an EV or want to learn more about an EV’s 12-volt battery, let’s start the conversation here.
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Why Do Electric Cars Need a 12-Volt Battery?
Just like in an ICE vehicle, EVs need a 12-volt battery to start.
The 12-volt system powers the starting circuit and the low-power computer systems that manage the high-voltage system. Pushing the start button activates a motor controller relay (or contactor, a powerful electromagnet). This allows power to flow from the high-voltage battery to start the vehicle and energize the electric drive motor.
A dead 12-volt battery cannot trigger the contactor, preventing an EV from starting, even if the high-voltage battery is fully charged.
Unlike an ICE vehicle, an EV lacks an alternator to recharge the 12-volt battery. Instead, the controller also manages a DC-to-DC converter that charges the 12-volt battery using the high-voltage battery. Called a step-down converter, the converter lowers the voltage from the high-voltage battery (400 or more volts) to the 14 volts needed to recharge the low-voltage battery.
An EV’s 12-volt battery also powers the accessories, lights, wipers, power windows and seats, heater blower fan, modem, airbags and other safety systems. You don’t need 400 volts to power the headlights or infotainment system, so you have a 12-volt battery to do that.
How Long Does an EV’s 12-Volt Battery Last?
On average, three to five years, similar to a 12-volt battery in an ICE vehicle. And, just like an ICE vehicle battery, how long a battery lasts depends on:
- Battery quality, since not all 12-volt batteries are the same;
- Driving habits (short trips vs. highway driving);
- Climate and environmental conditions;
- Battery and vehicle maintenance.
What Happens When an EV’s 12-Volt Battery Dies?
Stuff stops working. If the power doors won’t open, the key fob doesn’t work, the brake lights don’t come on or the vehicle doesn’t power-up/start, it usually signals a dead battery.
A dead 12-volt battery can be caused by lack of use. An EV’s low-voltage system is always ON, powering various computers and controlling modules, even when the vehicle is OFF. A courtesy light accidentally left on, a malfunctioning low-voltage charging system or a failing battery are also common causes of a dead battery.
Luckily, you can jump start an EV virtually the same time-honored way as an ICE vehicle.
Pro tip: According to NOCO technical support, you can use a battery maintainer on an EV 12-volt battery. Be sure to choose one compatible with EVs.
How To Know if the 12-Volt Battery on an EV Is Going Bad
If you jump start and charge the 12-volt battery and it keeps going dead, it’s most likely failing.
Other symptoms include dashboard warning lights coming on; interior and exterior lights, video or infotainment displays dimming or flickering; or accessories working intermittently or not at all.
EV 12-Volt Battery Maintenance
Required maintenance is basically the same as an ICE vehicle, including:
- Cleaning the battery, terminals and cables annually to increase battery life;
- Making sure all ground wires and cables are clean and tight;
- Ensuring battery is secure and held firmly in place;
- Replacing the battery with a new one if damaged or leaking fluid;
- Using a battery maintainer if the EV sits for extended periods.
Safety note: Leave ALL EV high-voltage battery and electrical service and repairs to the experts. Only a trained, certified technician wearing the proper protective equipment (PPE) should work on them.
