I believe that is an old fairy tale which dates way on back to old style
batteries, for whatever reasons, about storing a battey on concrete.I
don't see how it would have any effect at all on modern day
batteries.The main thing is to keep the battery charged up properly and
in my opinion, use the battery once in a while.
cuhulin

I've heard this on and off for years, and have never really been able
to figure out the physics of it either.  Some discussions in  urban-
folklore circles make me classify it as "ascribing false causality" to
a battery's natural loss of charge at a fractional percentage while
just sitting there -- exacerbated by any acid that leaked over the
case (batteries used to be leakier, especially up top, than they are
now).  Some people say that trapped moisture under the battery might
also help in the completion of a circuit.

(Even modern batteries leak a bit, as anyone can testify who has found
hidden corrosion under the battery tray in a car that's been in
service, with typical (lack of) maintenance, for several years or
more.)

It may have had even more of a basis in fact in olden times when a
battery involved a "battery jar" in a wooden case, but that was
donkey's years ago and probably has little to do with relatively
modern rubber or plastic cased batteries.
http://www.interstatebatteries.com/www_2001/content/faqs/tech_talk/maintenance/f
aq_tech_maint.htm

As someone points out in one such discussion at
http://msgboard.snopes.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=20;t=000695;p=1
there is also some likelihood that the battery was put on the floor
because it was unsatisfactory in some way in the first place,
whereupon it failed to get better with age.  See also
http://www.batteryuniversity.com/partone-13.htm -- in particular the
statement that "Lead-acid batteries must always be stored in a charged
state. {...} Prolonged storage below the critical voltage causes
sulfation, a condition that is difficult to reverse."  In other words,
the concrete isn't the killer of the battery, just its tombstone.

Those sites also have quite a bit of information on the care and
feeding of costly batteries that most people probably don't know, as
does
http://www.batteryfaq.org/

I might add that if a battery is  leaking a lot, it can uglify the
concrete (or pretty much whatever else you set it on), but a seriously
leaking battery needs secondary containment pending proper disposal
anyway.

Cheers,
--Joe

Sure it is a fact and does happen.  Batteries get a thin layer of acid
on them as they charge and discharge which comes from the vents or even
splashes from moving.  That is why you can burn holes in pants by
picking up a battery.

This layer, although thin will allow some current to flow over the
battery to the concrete floor which will discharge a battery over time
like a winter storage and leave a stain on the floor.

I tried an experiment with my electric boat batteries and left a couple
on concrete for a winter, the rest were on plywood.  The concrete ones
drained down, the plywood ones held.

And 'water witching' works really well!  I have found well sources and
can even find a blocked sewer pipe under a concrete floor or trace out
sewer pipes with running water in them!   Saves a lot of digging when
hooking up a new toilet or fixing trouble.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos:  Non members can still view!
Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
(More Off Road album links at bottom of the view page)

It's not a myth.What happens is this. Concrete by it's nature and
size/weight deadens vibration. It also maintains a more constant
temperature than other surfaces.

Those two factors lead to a battery that will over time allow
stratification of the chemicals of the battery much more readily
than a battery that gets moved around from time to time. This
stratification harms the battery.

My understanding of this practice stems from long ago when batteries were
made in glass jars. The fear was that if you set it on concrete you could
break the glass thus destroying the battery.

I personally store a couple of batteries on concrete and don't see any more
discharge in them than in cars that do not get driven much. Not scientific,
I know.

Any battery not in use needs to be charge every couple of months or so. I
charge my riding mower battery once a month in the off season. The original
battery lasted 13 years. My neighbor who does not charge his has to replace
his every couple of years. To get a full charge you need to take it to about
15.25 volts. I like to use a 1 amp charger for this.

OK... here's the explanation I've always heard....

The generation of electricity in a lead acid cell is an exothermic
reaction -- i.e. it generates(gives off) heat(and electricity) during
the chemical reaction. In theory, the battery comes to a steady state
where heat is generated(internally) and lost(thru the plastic case) at
the same rate. This means the "charge" is being lost even if the
battery is just sitting and not being used. Now, if you suck away heat
faster from the battery, you're sucking away charge faster. A concrete
floor or slab is almost the ultimate heat sink. You could put a lot of
heat into it without significantly raising the temperature. So the
battery heat is efficiently taken away quickly by sitting on the
concrete reducing the charge.

While the theory says this is true, I believe the actual effect to be
very small compared to many other factors including the air
temperature, the cell manufacturing tolerances and chemical tolerances.
I really don't think you could take two batteries, put one on a piece of
insulation and one directly on the concrete and expect any one to last
longer than the other every time...

Its a thermal effect. A concrete slab on grade is often cooler than the
surrounding ambient. Placing a battery on this surface cools the bottom
of the battery. The bottom half of the plates, being cooler than the
top, generate a slightly lower voltage. The top half of the plates 'see'
this as if its a battery with a lower charge connected in parallel. The
top half of the plates discharge in an attempt to recharge the bottom
half.

Since this circuit cannot be 100% efficient, net stored energy is lost.