Like internal combustion engine (ICE) cars, electric vehicles (EVs) have a 12V battery that is used to start the engine (or motor, in the case of an EV) and to power systems like the air conditioning, windscreen wipers, lights and so on.

In an EV, this 12V battery is separate from the high-voltage lithium-ion battery that drives the motor itself. Like in an ICE vehicle, the 12V battery is recharged when you go for a drive, but on an EV the battery can also gain some charge when your vehicle is plugged in.

Although it's quite unusual for an EV's 12V battery to go completely flat, it is possible. Potential causes include a worn-out battery that needs replacing, complete discharge (to zero per cent) of the vehicle's li-ion battery, or long-term storage without turning the vehicle on.

How to Keep an EV's 12V Battery Charged

Even the best electric car models will run flat eventually, if left turned off for too long, or if the 12V battery is poorly maintained.

During the first COVID-19 lockdowns, Ford issued guidance to their drivers suggesting one of the following steps if storing an EV for longer than 30 days without turning it on:

  • Disconnect the negative terminal of the 12V battery.
  • Leave the vehicle's charging cable connected and turned on.
  • Connect a 12V charger/booster to the 12V battery on a trickle charge.

Driving or charging your EV is the easiest way to keep the 12V battery topped up too: Ford said a minimum of eight hours of driving and/or charging in the past month is enough to keep a healthy 12V battery working.

Ford also recommends you keep your vehicle's li-ion battery at a minimum 10% charge during storage. The high-voltage battery should be fine for six months or more without maintenance, but the 12V battery will drain faster without maintenance, especially if you leave it fully connected to the motor.

Why Does it Matter?

In the past, you might have routinely boosted your ICE's 12V battery to get it to start on a cold winter morning, or if you don't drive very often.

On an EV things are slightly more complicated. The 12V battery is required to run the electronics that allow the vehicle to begin charging when you connect its cable — so if the battery is completely dead, you can't recharge it just by plugging your vehicle in.

You also should NOT try to jump start an EV using another EV. Neither the 12V nor the high-voltage battery on an EV is designed to provide enough power for another vehicle to start or to recharge from it.

If you attempt this, you risk damaging one or both vehicles' electronics and could void your warranty by using your vehicle as a static power source, as warned in the Tesla Model S Owner's Manual.

How to Jump Start Electric Cars

We strongly suggest that you contact your leasing provider and/or maintenance provider in the first instance before attempting this yourself as they may be able to send roadside assistance to you, depending on the terms of your contract.  

It is worth remembering that any damage caused from incorrectly jump starting your vehicle will not be covered by the manufacturer’s warranty or maintenance plan, and it is likely you will be liable for the cost of any repairs which could be extensive. 

If you want to try to jump start your electric car, at your own risk, , refer to your owner's manual or manufacturer's website to see if they provide specific instructions.

Make sure you follow their instructions, if any are available. That way, you can avoid damaging the electronics in your vehicle or voiding your warranty.

In general, the method to jump start electric cars is as follows. This is based on the directions provided in the 2020 Nissan LEAF Owner's Manual.

  1. Turn off your vehicle and disconnect its charging cable.
  2. Locate the terminals of its 12V battery — these might not be in the place you would expect if the car had an internal combustion engine (ICE).
  3. DO NOT try to access any high-voltage cables or systems, usually located behind bright orange shielding. You should not need to, and doing so can be very dangerous.
  4. Connect a standalone battery starter or connect to an ICE vehicle's 12V battery in the following way:
    1. Park the vehicles at a 90-degree angle with the batteries as close as possible.
    2. Connect a jump lead to the positive terminal on the EV's 12V battery.
    3. Connect the other end of the jump lead to the positive terminal on the ICE's 12V battery.
    4. Connect a second jump lead to the negative pole on the ICE's 12V battery.
    5. Connect the other end of the second jump lead to the grounded bodywork of the EV.
    6. Start the engine of the ICE (known as the 'booster' vehicle).
  5. Put the EV into its 'ready to drive' position.

If your EV does not start immediately, turn it off, wait 10-15 seconds and try to turn it on again.

Once the EV starts, carefully disconnect the battery booster or jump leads in the reverse of the order you connected them: body ground, negative pole on ICE, positive pole on ICE, positive pole on EV.

Keep your EV running for at least 20 minutes to put some charge into the 12V battery. At this point, if your vehicle's lithium-ion battery was completely discharged, it should be OK to connect to a charge point or charging cable to start topping up the high-voltage battery too.

Summing Up

The answer to "can you jump start an electric car?" Is yes, you can, but it is at your own risk and you will be liable for any costs if there are any issues or if it is done incorrectly. You will need an ICE car and traditional jump leads, or a dedicated battery booster.

The answer to "can you jump start FROM an electric car?" is no, you should not. Its electronics are not designed to do so, and you could void your warranty.

Keep both of those in mind and try to keep some charge in your 12V battery — at least enough to start charging the li-ion battery — and you should have fewer problems in the long run.