What happens to very cold but unused batteries?
What happens to very cold but unused batteries?
I'm considering buying an EV to replace my aging diesel. I live in a very cold country where temperatures regularly dip below -30C in the winter.
I understand that EVs lose range in cold temperatures and that they need heating to use and charge without damage.
My question is this: if I plan on not using my car for several weeks, can I leave it unplugged and/or tell it to stop managing the batteries' temperature to save energy and not damage the batteries?
I'm okay with spending half a day preheating it when I plan on using it again regularly, but I don't want it to draw current all the time for nothing when I'm away on long missions.
For some reason, I can't seem to find out if it's safe to keep a fully unpowered EV in the cold for a long time...
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Cold doesn't damage the battery. Batteries are basically electricity pumps. When they're cold they're less willing to give up their electrons. But being cold isn't inherently good or bad. It essentially reduces the efficiency of the pump.
Generally speaking the thing you want to avoid with ev batteries is getting them too hot. Heat damages them more than anything else.
The next temperature related thing is putting a heavy load on the battery when it's too cold. The important thing with this is a cold battery itself isn't necessarily bad, it's putting a heavy load on a cold battery that's bad
Also generally speaking, the healthiest state to store a battery is half charged.
If you'd like to read up on it the thing to search for is "lithium plating."
So long story short, if you're going to leave your EV for weeks at a time, the best thing you could do is leave it plugged in to a wall outlet and set the charge limit to 50%. Remember, EV batteries don't lose electricity when they're cold, they just can't pump all the electrons in them because they're cold. If you leave it plugged in and set the charger limit to 50% it'll maintain the battery at a good state of charge. It won't draw that much electricity either.
I know enough about Li-Ion to know that they don't like overcharging or undercharging, and even how they charge, since I'm an electronics engineer. But only at room temperature 🙂
What I didn't know is whether the cold alone damages them. You know, kind of like when living tissue gets damaged under the freezing point of water because ice crystals form and pierce the cells irreparably: I thought perhaps one of the chemicals in Li-Ion cells also migrated away from where they should be, or formed harmful solids or something that would damage the battery cell - without even pulling or pumping any current.
It sounds like it might be safe to leave the car in cold storage with only a trickle charge then.
Also, I spoke to a friend who has a plug-in hybrid (a rebadged Toyota RAV-4 I think): he says there's a control that he can set to warm, cool, auto or off for the battery pack temperature control, and he recently left his car parked at the airport for several days on off with the temperatures below -13F. So I'm guessing it must be okay to do that. Also, apparently his hybrid gives up and simply refuses to run on batteries below 10F, so I'm guessing the battery pack warmer isn't very powerful and it's not too critical to let it go cold.