Do electric cars’ batteries drain when not in use?

Sometimes, life dictates that your vehicle be parked for an extended period, without so much as moving a wheel. So, what happens if you leave your electric car standing for a few weeks or even months on end?

The question is a fascinating one that came to the fore in South Africa when the country was suddenly locked down in 2020, seeing electric vehicles (EVs) standing idle in garages and on driveways across the land.

Global pandemics aside, EVs are also parked up when their owners head overseas on business trips or embark on long-distance local holidays. Volvo XC40 P8 Recharge buyers, for instance, enjoy the use of a petrol-engine car for two weeks per year.

The Citizen Motoring has done a bit of research and will try and answer all the uncertainties around batteries when an electric car is standing longer than usual.

Can an electric car’s battery drain by itself?

The short answer is yes, though far less and at a far slower rate than you probably think. While every type of rechargeable battery is prone to self-discharging over time, they’re certainly not all created equal.

Such is the efficiency of the lithium-ion packs used in most modern electric cars, you can expect it to lose only a couple of percentage points of charge per month in the most favourable conditions.

It’s this high efficiency and low self-discharge rate that makes fully electric cars fitted with advanced lithium-ion packs perfectly capable of standing idle for weeks at a time. Nickel-metal hydride batteries, by contrast, self-discharge quite a bit faster, should a couple of conditions be met. We’ll touch on the latter shortly.

What causes the battery to discharge?

Interestingly, an electric car’s conventional 12V (often lead-acid) battery is what directly powers low-voltage electrical ancillaries such as the alarm, central locking system and the vehicle’s various electronic control units. Since these systems usually remain active to a degree even when the vehicle is parked, they can accelerate the lithium-ion pack’s discharge, since the 12V item relies on the traction battery for power.

It’s a similar story with connectivity features. Though in the Volvo XC40 P8 Recharge‘s case, systems that have contact with the Volvo Cars app are programmed to shut down when the vehicle is not used for “extended periods of time” in order to save the battery. So, carmakers have clearly thought about the potential problem of batteries self-discharging and implemented solutions.

Still, the impact of ancillaries remaining active in the background is fairly minimal. This is illustrated by the fact that the typical electric car is able to preserve its state of charge exceedingly well even when stuck at a standstill in traffic for hours on end, with far more power-heavy accessories such as air-conditioning running.

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How do you keep a parked EV’s battery healthy?

One general recommendation is to make sure the EV isn’t exposed to very high temperatures as this tends to speed up the rate of discharge.

It’s also worth activating the electric car’s energy saving mode and deactivating any pre-conditioning settings that may be in place.

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Manufacturer recommendations vary greatly when it comes to the ideal state of charge for storing a vehicle. Some suggest a charging target of 80%, others specify a number between 30% and 60% and some say no more than 50% is best. While a couple more advocate for leaving the vehicle in a fully charged state, others advise such an approach could lead to battery damage, greatly decreasing the pack’s usable capacity.

In short, it’s best to follow the guidelines provided by each specific EV’s manufacturer. All, however, seem to agree leaving an electric car battery empty for an extended period is to be avoided.

Should I leave my electric car plugged in?

Again, the answer to this question varies between manufacturers. American manufacturer Tesla, for instance, recommends leaving the vehicle plugged in if it won’t be driven for “several weeks”, while others strongly discourage such an approach to long-term storage. Some furthermore suggest using a trickle charger to keep the 12V battery suitably topped up.

Ultimately, you can rest assured most electric cars can quite comfortably handle prolonged periods of inactivity, arguably even better than their combustion-engine counterparts. As always, though, it pays to follow the guidance provided by the manufacturer in the specific vehicle’s handbook.