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June 26, 2009

Car Talk

The garage floor isn't to blame when a car battery loses its charge

Syndicated columnists

Dear Tom and Ray:

My son, who transports cars for a living, says that we should not put a car battery on the garage floor for more than a few moments while we're moving it from one place to another. In other words, we should never store it on the garage floor. Why? He claims that it will discharge. He says it happens to them all the time. Now, I'm an electrical engineer. Nothing in my knowledge, training or experience tells me anything about cement garage floors being in any way, shape or form conductive, or in any way a cause of battery discharge. Which one of us is nuts? --Tom

Ray: Your son is. We've always been told not to leave car batteries on garage floors, too. But that's so other mechanics won't trip over them and crack their
heads.

Tom: Cement is not conductive. You're right about that. But any rechargeable battery -- that's left anywhere -- eventually will lose its charge. Rechargeable batteries are particularly quick to discharge. Just like your cell phone's battery runs down when it's sitting on the kitchen counter overnight.

Ray: There are some people who have told us that this old myth comes from the days when battery casings were made out of wood. If the battery acid
spilled out, it could make the wood wet, and create a conductive path to a moist cement floor. I wasn't around when batteries were made out of wood, so I don't know. My brother was around, but nowadays, he can't remember anything before the Teapot Dome Scandal.

Tom: Another theory is that garage floors are simply colder than, say, workbenches. And, as every electrical engineer knows, chemical reactions slow
down in lower temperatures. So, while the battery might not be discharging on the cement floor, it might be cooling off, and be less able to pump out its power temporarily.

Ray: That's why we store all of our unsold batteries on our living-room sofas, Tom. Tell your son that's what he needs to do, too.

(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk Web site.)

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