How Long Can an Electric Car Just Sit There?

Cars are meant to be driven. When a typical vehicle sits unused for weeks or months on end, it begins to atrophy in all sorts of ways. Tires slowly lose their air pressure. Car batteries lose charge and might eventually need a jump-start. Oil and other fluids lose their ability to lubricate when they get stale, while gasoline starts to go bad after about a month. Eventually, nature tries to reclaim a vehicle via pest infestation, accumulating bird poop, or meteorological act of God.

This collection of potential misfortune is why collectors make sure to turn on their barely-driven cars every once in a while. It’s why you might ask your friend to drive your car around the block a couple of times a month when you plan to go away for a long stretch.

Are the rules still the same in the era of electric vehicles? Although EVs have neither an engine nor many of the fluids and parts that come with a gas-burning car, it turns out that electric vehicles don’t do well sitting still for long periods of time, either. The technology under the hood is radically different, but the underlying truth is the same: It’s best not to let the car sit undriven for too long.

Electric cars have one untouchable advantage when it comes to long-term storage: You can just leave them plugged in. If you can do this — even by running a ridiculously long extension cord from a standard outlet — then the car will use this trickle of juice to maintain its battery health and keep its systems ship-shape.

If you can’t leave your car plugged in, though, the first thing to worry about is the EV’s main battery going dead. The giant lithium-ion units in today’s electric cars are really good at retaining charge, but they’re not perfect: An EV sitting still will lose a little bit of juice at a slow, steady rate, perhaps a couple of percentage points over the course of a month. You don’t want to leave your car with barely any charge and return from a trip to find out you killed its battery, especially when letting the unit hit zero could potentially damage it.

This concern is enough to make me fill up my EV to at least half before a flying vacation — that way I don’t have to nervously open the Tesla app to check how many miles are left on the car. But as long as you exercise a modicum of common sense, that shouldn’t be enough to get you in trouble. An electric vehicle with at least 50 percent charge could go many, many months before its charge rate dropped to a worrying level. General Motors tells Heatmap that for its current slate of EVs powered by Ultium batteries, it recommends having at least 30 percent charge on the battery before putting the car into long-term storage.

However, an EV’s main battery isn’t its only one. Before electric vehicles went mainstream, the term “car battery” meant the 12-volt box you’d see for sale at Auto Zone or under the hood of any normal vehicle — the one with the two posts where you’d hook on jumper cables. EVs have these smaller batteries, too. They’re there to handle low-power applications such as the doors and windows in case the main battery dies, and they’re one of the principal worries when it comes to leaving an EV sitting still.

Just like with a gas car, the 12-volt battery in an EV doesn’t like to sit dormant while you take a months-long vacation overseas. GM says the car will monitor the health of both batteries and use energy from the big one to keep the small one from dying — up to a point. If the high-voltage battery gets too low, it stops supporting the 12-volt.

It is possible to disconnect the 12-volt battery if you have the electrical know-how, but your car’s user manual will probably tell you not to. Instead, GM recommends that before you store the Chevy Bolt for a long stretch, you attach a trickle charger to the positive and negative poles of the battery under the hood. The trickle charger is a longstanding gadget that can be used to revive a dead car battery, or, in this case, to prevent it from dying while you’re taking the train across Europe. With it attached, the little battery doesn’t need to steal juice from the big one.

Think, too, about where you’re leaving that EV sitting around. Batteries don’t like extreme temperatures, and bitter cold or insufferable heat could not only sap battery life but also potentially damage the unit. Like traditional cars, EVs are safer stored inside a garage if possible — not sitting around the front yard like a project car.

And one more thing before you leave town: Don’t forget to hide the key fob at least 10 feet away from the car, GM says, lest you accidentally leave the vehicle unlocked.