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.
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As someone points out in one such discussion at
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is also some likelihood that the battery was put on the floorbecause it was unsatisfactory in some way in the first place,whereupon it failed to get better with age. See also
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-- in particular thestatement that "Lead-acid batteries must always be stored in a chargedstate. {...} Prolonged storage below the critical voltage causessulfation, 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
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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