Is it OK to Disconnect the Battery for Eight Months?

Dear Car Talk

Dear Car Talk | Dec 16, 2014

Dear Car Talk:

We have a Subaru Outback and a Toyota Prius. As soon as there are more charging stations around, we plan to get a Tesla Model S electric car. We have a pop-up trailer from which, when not in use, the battery is removed and hooked up to a battery charger. To my surprise, the charger has kept the battery charged very well. When we get the Tesla S, the Subaru would be used only for winter driving and for vacations where we would have to tow the trailer. My question is: If I take the battery out of the Subaru for roughly eight months of the year, would it negatively affect the electrical system or anything else on the Subaru?

-- Vinnie

No, Vinnie. If you take the battery out of the Subaru, the only real danger is that you'll trip over it in the garage. So, alternatively, you can just disconnect the battery and leave it right in the car.

And I wouldn't bother keeping it on the charger for eight months -- you'd just be wasting electricity. If you have a good charger, you can just hook it up the day before you need the car, and the battery should be fine by the next day.

That also reduces the risk that something would go wrong with the charger and it would burn down your house while you're gone.

When you reconnect the battery, there are a couple of inconveniences you'll have to deal with, besides the obvious stuff like losing your radio presets.

Most modern cars have computers that "learn" and adapt the engine and transmission to your driving style. So those settings will all be lost, and the car will have to "relearn" them. That means you may notice the car running a little poorly or shifting a little roughly at first. But it'll go away quickly.

The other thing to keep in mind is that if you have a new or freshly "back from the dead" battery, you won't be able to pass a state emissions inspection until you drive the car for several drive cycles.

During those drive cycles, the computer is checking various components of the emissions system in your car. And only when it has enough data will it report a passing grade to the inspection shop. Typically that means you'll have to drive the car for a few days before getting it inspected.

My brother and I used to recommend all kinds of other things to people who were storing vehicles for months (squirting oil in each cylinder, covering the tailpipe and intake manifold), but we gave up on that, because nobody ever bothered with it. And in the vast majority of cases these days, the cars start and run just fine after being stored, anyway.

So just disconnect the battery, and don't forget to roll up the windows. Good luck, Vinnie.


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