Asimov wrote:

I had it explained to me that the difference in temperature between
the cement and ambient air causes a vertical specific density
difference in the electrolyte. This effect results in an a emf between
the top and bottom of the plates which being conductive allows the
usual battery chemical reaction to take place. Thus the battery
slowly discharges over a period of many months (6 or more).

Are we still hashing through this? Did I miss the post where it said
"Check with the battery manufacturers" or "Check with someone who
actually knows"? This myth is so pervasive that most battery
manufacturers include it in their FAQ section. The universal statement?
Storing on concrete does not increase the self-discharge rate of a
battery, unless the battery is in a wooden case, ca. 1910.

http://www.exideworld.com/faq/faq_marine.html#concrete
http://www.trojanbattery.com/Tech-Support/FAQ.aspx
http://www.ibsa.com/www_2001/content...tech_maint.htm
http://www.uuhome.de/william.darden/...4.htm#concrete
etc etc etc

Or just Google "lead-acid battery concrete discharge" for 38,000 hits on
how this is not true.

Bill