Do batteries need to be set a a rubber mat in the garage?

Dear Car Talk

Dear Car Talk | Apr 01, 1999

Dear Tom and Ray:

I am a middle school science teacher who is questioning a time-honored
warning handed down to me from my grandfather. My wife and I were cleaning
the garage when I was shocked to see a car battery resting on the concrete
floor and not resting on wood. Pat, my wife, said, "What difference does it
make?" My response was that the cement would drain the battery. Luckily for
me, she didn't ask how, because I would have been stumped. Can the cement
drain the battery, and if so, how? -- Dave

TOM: Well, Dave, you're a model for middle school science teachers
everywhere. Why? Because you didn't try to fumble around and make up an
answer like I would have!

RAY: You can completely ignore your grandfather's warning these days, Dave.
In his day -- even in your father's day -- most battery casings were made
of hard rubber. And because of the porosity of that material, battery acid
would sometimes seep through the rubber and create a conductive path
through the damp concrete, draining the battery.

TOM: But that can't happen today with plastic-cased batteries (which we've
been using exclusively since about the time Nixon said, "I am not a
crook"). That's because molded polypropylene (a k a plastic), as you
probably teach your students, Dave, is not porous at all.

RAY: And here's the interesting thing, Dave. The cooler the temperature,
the slower a battery's rate of discharge. And because concrete is often
cooler than its surroundings, leaving a modern battery on a concrete floor
might actually make it last LONGER than leaving it on a wooden pallet! How
do you like them apples?

Copyright (c) 1999 by Tom and Ray Magliozzi and Doug Berman
Distributed by King Features Syndicate, Inc.

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