Can You Jump-Start an Electric Car?

What you cannot do is jump-start the high-voltage battery. That's not a job for jump leads under any circumstances.

Why an EV has two batteries

The large lithium-ion pack under the floor drives the wheels. Separately, there's a conventional 12V battery, much like the one in a petrol car, which runs the low-voltage systems: lights, wipers, infotainment, central locking, and importantly the electronics that wake the car up and connect the main pack.

If the 12V battery is flat, the car can't complete that wake-up sequence. So you get the odd situation of an EV with a nearly full traction battery that won't do anything at all.

How to jump-start the 12V battery

The process is the same as any car, but check the handbook first, because access points vary and some models have dedicated jump terminals rather than an exposed battery.

1. Locate the 12V battery or the designated jump-start terminals. On many EVs it's under the bonnet, on some it's in the boot or under a panel.
2. Use another vehicle or a portable jump pack, with the donor engine off initially.
3. Connect red to the positive terminal on both, then black to the donor's negative, and the final black clamp to the designated earth point on the EV rather than directly to its battery negative.
4. Start the donor car, or switch on the jump pack, wait a minute or two, then try to power up the EV.
5. Once it's awake, the car's DC-to-DC converter will normally start recharging the 12V battery from the main pack.

If it works but the problem recurs within days, the 12V battery is probably at the end of its life and needs replacing. They typically last three to five years, same as any car battery.

What you must not do

Never attempt to jump the high-voltage battery. It operates at several hundred volts and is not accessible with jump leads. If the traction pack is flat, the answer is charging or recovery, not jump-starting.

Don't use your EV to jump-start another car. Many manufacturers explicitly prohibit this. The EV's 12V system is designed to be topped up by the main pack through a converter, not to deliver the large current a petrol engine's starter motor demands, and you risk damaging the converter. Check the handbook, but treat "no" as the default.

Don't guess at terminals. Some EVs are particular about where the negative clamp goes. Getting it wrong can damage sensitive electronics.

Why 12V failures are so common on EVs

There's an irony here. EV owners often report 12V trouble more often than petrol drivers, for a few reasons.

The 12V battery is doing plenty of work while the car sits, keeping systems on standby, running connectivity, and waking periodically. Meanwhile a petrol car's alternator gives its battery a solid charge on every drive, whereas an EV tops the 12V up in a more measured way.

Cars that sit unused for long periods are particularly prone. If you're leaving an EV parked for weeks, it's worth leaving it plugged in where possible.

What this means when buying used

If a used EV is slow to wake, has flickering electronics, or the seller mentions having jump-started it recently, that's usually a cheap 12V battery issue rather than anything sinister about the main pack. It's worth a small negotiation but it isn't a reason to walk away.

The genuinely expensive risk sits with the traction battery, and that's the one you can't diagnose by turning a key. That's what a State of Health check is for.