P Buckmaster, Co Dublin asks: “I keep hearing that if you don’t drive daily, an EV is bad for you as infrequent driving shortens the life of the battery. They’re not supposed to be left idle for days. I’ve never seen that written about. Is it true?”
This can be a potentially tricky one, especially given the lack of places to leave an electric car plugged in for extended periods of time – such as in the long-term car park at an airport.
Even when an EV is switched off, it does still draw a tiny bit of power from the battery. That’s because cars still need power to run systems such as keyless entry (which requires sensors to be active to detect when the key is approaching), and background tasks such as software updates or specific systems such as ‘sentry mode’.
The power drain isn’t massive – on average it’s about 1 per cent per day – but if your car has a relatively small battery, or you’ve parked up with half a charge left, it can become an issue over time. You may come back from a few weeks away to find that there’s not enough charge left in the battery to get home. Or worse, you could come back to a ‘bricked’ car that doesn’t have enough charge left in it to even open the doors.
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This can also be an issue for an electric car’s onboard 12-volt battery. Yes, for all the technological mastery of the big lithium-ion and lithium-iron phosphate batteries stashed under the floors of our EVs, they all still have regular old 12-volt batteries on board for powering minor systems such as heated seats, heated windscreen and rear window, and – yes – central locking.
Just as with an internal combustion engine, that 12-volt battery is kept topped up by driving the car around – whereas petrol and diesel cars use their alternators to divert any excess energy to the 12-volt battery, electric cars do it with spare energy from the big ‘traction’ battery. If you’re not driving, that 12-volt battery can be a constant source of drain on the big battery, as it’s always switching on and asking to be topped up. Equally, if the 12-volt battery drains and doesn’t get charged up, you’re coming home to a car with dead central locking.
[ Can I really do a long journey in an electric car?Opens in new window ]
So, you should definitely leave your EV plugged in while you’re away, right? Ah, possibly not...
The thing is, it kind of depends on the car, so the best thing to do is to check with your dealer as to what’s the best course of action (and hope that they’ve been properly trained to deal with such queries).
Some car makers – notably Hyundai and Kia, but there are others – say that leaving one of their electric cars plugged in for long periods is fine, because the sophisticated battery management systems can deal with that and you won’t get into an issue where the battery isn’t constantly draining and then topping-up its last one per cent of energy storage, something which would definitely cause excess wear and tear to the battery.
[ EV Q&A: Why are there no lamp-post chargers in Ireland?Opens in new window ]
However, other brands – Nissan among them – say that you should definitely not leave their EVs plugged in for long periods of time, for precisely the reasons mentioned above.
If you are going to leave your electric cars plugged in while you’re off on your extended business trip or backpacking around the Amazon, the best thing to do is to make sure you use the charging settings control either on the car’s touchscreen or through the cart’s connected smartphone app, and make sure that you set the battery to charge up to no lower than 50 per cent, and no higher than 80 per cent.
It also makes a difference where and how the car is stored. Excessive heat or excessive cold can cause further complications by speeding up battery discharge, so if possible try to stash your EV in a garage while you’re gone. Not everyone will be able to, of course.
Mind you, much of this advice is kind of based on worst-case scenarios. For the most part, it’s absolutely fine to leave your EV sitting for an extended period. In fact, as many car makers point out, as long as the battery isn’t being exposed to constant 40-degrees Celsius or more while it’s standing, there really ought to be no major issues.
According to Renault’s expert battery team: “While the batteries in electric cars, cell phones, and computers all use the same lithium ion technology, the high quality of the battery cells used in automobiles is a world apart. The self-discharge of the battery in an EV, in other words the loss of charge when the car is parked but not plugged in, is imperceptible over time.” You probably can’t say the same for your smartphone...
Or maybe, we should just start thinking of our EVs as being rather like pets. You wouldn’t, after all, head off for months at a time, even weeks at a time, without making sure that a trusted friend or relative was stopping by to feed the cat or walk the dog. Perhaps this is a future employment opening in the electric motoring world: dog walker, cat feeder and electric car exerciser.
