With electric vehicles (EVs), most of the talk is about the high-voltage battery that drives the motor. How long do they last? How expensive are they to replace? How many miles you can travel between charges? And what happens to them once they reach end-of-life?

You may not know EVs come with a good old-fashioned 12-volt lead-acid battery. (Tesla uses a lithium-ion 12-volt battery.) Like its internal combustion engine (ICE) cousin, an EV will not start if its 12-volt battery is dead.

Luckily, jump-starting an EV 12-volt battery is virtually the same as jumping an ICE vehicle battery, with some really important safety considerations. Here’s what you need to know before throwing away those jumper cables.

Why Do EVs Have 12-Volt Batteries?

To power the accessories, lights, wipers, power windows and seats, heater blower fan, modem and airbags. It also powers the starting circuit and low-power computer systems that manage the high-voltage system.

Pushing the start button activates the motor controller relay (or contactor, a powerful electromagnet). That allows power to flow from the high-voltage battery to start the vehicle and electric drive motor.

Because EVs don’t have an alternator, the controller also recharges the 12-volt battery. A dead 12-volt battery cannot trigger the relay, which keeps an EV from starting, even if the high-voltage battery is fully charged.

How Do I Know the 12-Volt Battery Is Dead?

Just the same as on a traditional vehicle. If the power doors don’t open, the key fob doesn’t work or the brake lights don’t come on when depressing the brake pedal, it usually signals a dead battery.

A dead 12-volt battery can be caused by an EV sitting unused for a long time. The low voltage system in most newer vehicles is always “on,” powering various computers and control 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.