3 days ago
Can I leave an electric car unattended for a long time?
Dear Alex,
I live in the UK, but I am away for up to six months. I am considering buying a small electric vehicle as a runaround. How long will a fully charged electric car hold its charge? What happens if the battery is left to go flat? Is this bad for the battery, and will I lose all the computer information etc? How should I get it ready for use after such a long absence? Finally, is it safe to leave a car on charge for up to half a year?
– PN
Dear PN,
There are no hard and fast figures on how quickly an EV battery will lose its charge, but most of the experts I've spoken to reckon a battery will lose one or two per cent of its charge each month.
If you're going to take an EV off the road for a longer period, it's generally agreed that it's best to charge it to 80 per cent, which is better for long-term battery health than a full charge.
By doing so, even at a rate of two per cent loss each year, it would still take just over three years to flatten the battery completely.
Even then, the battery wouldn't be entirely dead, because even when an EV reads zero, there's still a little bit of charge left – manufacturers tend to leave a small margin because flattening a battery completely is not good for its long-term health.
So if you leave the car with 80 per cent charge for a few months, you should still have a healthy amount remaining when you return. I wouldn't recommend leaving it on charge on a three-pin socket all that time, however, three-pin sockets aren't designed for continuous high power use, so while charging that way is fine on occasion, I wouldn't leave a car plugged in for that length of time.
In terms of getting the car ready for use, disconnecting the 12V battery (which powers the ancillaries) before you leave is a good idea, as parasitic drain will almost certainly flatten it while you're away. You may lose some of the settings on the car's computers, but otherwise you shouldn't see any ill effects.
If you don't fancy that, you could instead use a trickle charger to keep the battery topped up. Also, increase the tyre pressure – to 50psi, say – to avoid flat-spotting, but remember to return the pressures to normal before you drive.
