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Hybernating our Hybrid

Disconnect or trickle-charge your battery when you mothball your carWe know from seeing all the tow trucks running through our neighborhood since Coronavirus quarantine that old-fashioned combustion cars won’t start after a couple of weeks, but it’s kind of ironic that an electric car won’t start either. Yep, electric, hybrid and plug-in hybrid cars have two batteries: a “drive” battery that moves the car, and a “start” battery that handles the various systems in the vehicle, like the drive computer.

To add to the fun, the batteries have different chemistry: the drive battery (Lithium Ion) should be charged to between 25% and 75% and will stay safely in that range for a year; but the house battery (Lead Acid) will discharge quickly and be permanently damaged if it does. If you’re going to put your vehicle in long-term storage, you either have to disconnect the start battery, put it on a trickle charger, or replace it when it’s time to drive again.

Don’t just plug it in

If you leave your electric or plug-in hybrid plugged in, it will fully charge the drive battery (which will damage it over time). If you don’t plug it in, it will fully drain the start battery (which will damage it over time).

The Tesla is the exception to the rule. You can set your Tesla to complete charging at (say) 75% and leave it plugged in.

Our Volvo XC90 T8 has no such feature. You have to “drive it around” or “plug it in” until the drive battery is around 25%, and check it every six months; they have no guidance for the start battery. The manual says:

plug in your car but not too much
If the state of charge is high – run the car until approx. 25% remains. If the state of charge is low – charge the battery until a level of approx. 25% is reached.

To minimise hybrid battery degradation during prolonged storage (longer than 1 month) of the vehicle a charge level of approximately 25% is recommended as indicated on the driver display.

Trickle Charger

Solar Trickle Charger for 12V BatteriesWe got a cheap simple trickle charger from Amazon a couple years ago and it’s now on its third car. They also make solar-powered trickle chargers that clip directly to your battery or, if your car supports it, you can put it on your dashboard and plug it into the cigarette lighter.

How about a Cover?

Really important: if your car is parked on a public street (or in some cases even in your driveway) you must put the licence plate number on the front and back or supply a window.

We got a basic cover for our car, suitable for Southern California.

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