How to store an electric car long-term
It’s easy to think that leaving an electric car standing for long periods would require nothing more than plugging it in, locking it and walking away. And you may well get away with that.
But if you have any reason to leave your electric or plug-in hybrid car idle for a long period – such as the current government-imposed coronavirus lockdown – it’s worth taking a few simple measures to maintain both the high-voltage (HV) battery and the 12v battery that powers the ancillaries.
More on that in a moment. First, in terms of keeping the car’s main battery in good condition, you’re best off not leaving the car plugged in for long periods. Just make sure it has a good amount of charge in it – ideally 80% or more – and then unplug it.
Coil the cables neatly but loosely so they don't get kinked. It’s always worth making sure that cables are stored somewhere dry where they won’t be dropped or generally knocked about, as that can damage the plugs.
Finally, locate the 12v battery in your car. It's far more likely that you’ll have problems with a flat 12v battery than any issues with the main lithium-ion battery pack.
The 12v battery in electric cars is exactly the same lead-acid battery that you may be used to seeing in petrol and diesel cars and it can lose charge gradually over prolonged periods, just as it will in any car.
To avoid a flat battery, make absolutely sure that the car is switched off before touching the battery and always wear protective gloves. You’ll need a spanner or socket to loosen the nut holding the cable to the terminal.
Always disconnect the negative terminal first – it’s normally a black cable. Then disconnect the connector from the positive terminal (normally a red cable) and make sure both cables are tucked away safely so that they don’t touch any metal part of the battery or vehicle.
You can leave the 12v battery in the vehicle while it’s standing, just make sure that it’s dry and that the cables can’t come loose and make contact. It’s better – if not essential – to store this lead-acid battery indoors rather than leaving it in a car that’s stored outside, as temperature changes aren’t friendly to battery charge and condition.
Alternatively, a trickle-charger (an inexpensive purchase from any good car parts store) can be used to maintain charge in a 12v battery in an electric car, but the car will need to be parked in a garage with access to a domestic socket.
If the 12v battery does go flat, you can jump-start it from a normal petrol or diesel car, or from a portable power pack, using standard jumper cables.
You must not jump start another car from an electric car or plug-in hybrid, however, as that can damage the electrics in the plug-in vehicle. Always check the owner’s handbook regards jump-starting, as manufacturer advice varies between brands.