Here is a little something I picked up at the Urban Legands homepage -
hope this will answer any questions you might have on batteries and
concrete floors:
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This was actually explained in good detail on cartalk.com by Tom and Ray
Magliozzi, the car talk guys, in their newspaper column #6980. You can find
the column at http://www.cartalk.com/Columns/CC/CC6980TXT.html.
I have copied it below:
Dear Tom and Ray:
My wife drives 15 minutes to work five days a week. After a
recent vacation when she didn't drive the car for a few weeks, I found the
battery dead. I took the battery out and trotted up to the local service
station, which shall remain nameless. I say this because the man wearing the
star took my battery, put it on the bare, concrete floor where the charger
was, and connected the charging cables. A heated discussion proceeded
between the two of us about the lack of a piece of wood for insulation
between the battery and the floor. I have taken enough mechanic classes in
my life now to remember being cautioned to never place a battery that you
wanted to use again on the ground. Be it dirt or concrete, the battery's
life would be shortened. Being told that it had something to do with the
earth's mass being negatively charged was always enough for me to accept
this rule of thumb. BUT, the star man told me I was a fool for believing
this absurd and unproven concept. What is your learned opinion? I'm on the
verge of losing sleep over this issue. -- Ballan
Tom: I actually see two issues we need to address, Ballan. One is
why it's OK to leave a car battery on a concrete floor, and the other is
how you're going to apologize to this gas-station mechanic whose mother you
probably insulted during this argument.
Ray: While there used to be some basis for not leaving a battery on
the floor, it doesn't really apply anymore.
Tom: If the outside of a battery is covered with acid -- on the
sides and the bottom -- then the moisture in the concrete (or in moist dirt,
I suppose) could serve as a conductor, and could increase the rate at which
the battery drains.
Ray: But even at that, you wouldn't expect to see any real change in
the battery's effectiveness for many weeks.
Tom: Moreover, you just don't see batteries covered in acid these
days because most batteries are maintenance-free, and they're sealed up
pretty tight.
Ray: The only way you could make that kind of mess on a maintenance-
free battery would be to severely overcharge it and make the acid bubble
over onto the casing.
Tom: So this "rule" about leaving batteries on the floor made a small
amount of sense before maintenance-free batteries, but it hardly applies
anymore. In fact, a battery manufacturer near us says that during the summer,
they store their new batteries on the concrete floor because it keeps
them cooler, and therefore helps them PRESERVE their charge.
Ray: Now let's address the second issue: how you're going to prevent
this guy at the local gas station from pouring Mountain Dew in your gas
tank next time you come in. We know you told him in no uncertain terms what
a stupid moron he is, and now, you need an elegant way to back down.
Tom: Here's what you do. Tell him you didn't want the battery on the
floor because you were afraid he might trip over it and hurt himself, and
you were only looking out for his best interests. Good luck, Ballan.
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Although I was not able to find it on the Urban Legends page, I also seem
to recall that the old addage about car batteries and concrete floors had
to do with older batteries having cases covered with tar. Why that makes
any difference I can't for the life of me remember, and since I couldn't
find a reference to it anywhere, it's probably just something I learned in
a dream.
Mark
"But what I really want to know is what will happen if I take the guest
towels from the bathroom without telling my wife and put them on the
concrete floor while I'm changing the oil in my Triumph..."
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Dr. Mark Clark
Oregon Institute of Technology
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