Since You Asked: Battery vs. the floor

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I had a car battery charged the other day and it was sitting on the sidewalk and a neighbor told me the sidewalk would drain the battery. He said somebody once explained this to him, and that it was no joke. Is he having me on?

— John V., Medford

We had to go to the little battery shop out behind the Vocational Division of the Since You Asked Institute of Automotive Technology to get the goods on this one, John.

The notion that a concrete floor will drain a modern battery is an urban myth, but it does have some historical basis. A battery that sits in your garage for months, say for the winter, will lose some or all of its charge. Not because it's on the concrete floor, but because it's designed to be frequently charged by an alternator in a car being driven.

And decades ago, hard rubber battery cases with a high carbon content would allow a battery to drain if the concrete floor permitted the current to find an electrical ground. The standard wisdom of those days — don't store batteries on concrete — still gets passed along, even though it doesn't apply to modern batteries.

Even earlier, batteries came in a glass jar inside a wooden case. Moisture on the floor of a shop or garage could cause the wood to swell and fracture the glass, causing the battery to leak.

Send questions to "Since You Asked," Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by e-mail to youasked@mailtribune.com.

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