Why does an electric car still have a 12V battery?
Because the entire ecosystem of automotive electrical components runs on 12 volts, and the high-voltage traction battery is deliberately disconnected whenever the car is not in use.
What the 12V battery powers: the door locks and the fob receiver, the lights, the dashboard displays and infotainment, the wipers, the airbag and safety systems, the alarm, and — crucially — the contactors that connect the main traction battery to everything else.
The chicken-and-egg point. The high-voltage battery is isolated by contactors when the car is off, for safety: hundreds of volts sitting live in a parked vehicle would be dangerous to occupants, to anyone in a collision, and to emergency responders. Something has to close those contactors, and that something needs its own independent power supply. That is the 12V battery's central job.
Why not redesign everything for high voltage? Because the industry has a century of standardised 12V components — motors, sensors, switches, bulbs, relays — available cheaply and proven. Redesigning all of it would be enormously expensive for no functional gain. Low voltage is also safer to work on and subject to far less onerous insulation and safety requirements.
How it is kept charged. A DC-DC converter steps down from the traction battery to charge the 12V system whenever the car is on or charging. There is no alternator.
Why it still goes flat, which surprises owners:
Parasitic drain. Connected cars run telematics, remote apps and scheduled wake-ups, all on 12V.
Long periods unused, particularly in cold weather.
Age. Conventional lead-acid batteries degrade on the same timescale as in any car.
A flat 12V battery immobilises the car completely even with a full traction battery, because the contactors cannot close. This is the most common EV breakdown call, and it causes disproportionate frustration because the car has plenty of energy it cannot reach.
What to do about it: most EVs have jump points under the bonnet, and can be jump-started from another 12V source — but never use an EV to jump-start another vehicle unless the handbook permits it. Some newer models have moved to lithium 12V batteries or integrated the function differently.