It surprises almost everyone: a fully electric car also carries an ordinary 12 volt lead battery. And when that one is flat, the car does nothing at all — however full the traction pack is.
Why an EV has a 12V battery at all
Everything that runs on 12 volts in a normal car runs on 12 volts in an EV too: central locking, the on-board computer, the screens, the lights, the steering assist and, crucially, the contactors that switch the high-voltage pack on. Without 12V those contactors stay open, so the car literally cannot reach its own traction battery.
Why it fails sooner than you expect
In a petrol car an alternator charges the battery whenever the engine runs. An EV has no alternator: a DC-DC converter draws from the traction pack, but only while the car is awake. Standing still for long periods means little charging while the electrical system keeps running for alarm, connectivity and preconditioning.
How to recognise it
The car does not respond to the key or the app, the screen stays black, or a 12V system warning appears. Sometimes the doors still work but the car will not go into drive.
What not to do
Do not work on the high-voltage side yourself. The orange cables carry lethal voltage and ordinary tools offer no protection.
What we do
We replace only the 12V battery, wherever the car is parked, following the manufacturer's procedure, and register it where the car asks for it. We do not touch the high-voltage pack.
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