| Older style batteries using porous rubber cases can ground to concrete; and you are correct about your theory of temperature differences, although I am not sure there are any measurable affect on our car batteries unless the temps are dramatically different. From the website: BatteryFAQ.Org - Will storing batteries on a concrete floor will discharge them? "All lead-acid batteries will naturally self-discharge which can result in loss of capacity from sulfation. The rate of internal self-discharge is most influenced by the temperature of the battery's electrolyte and the chemistry of the plates. Heat speeds up this self-discharge, so do not store batteries in a hot garage or warehouse. This internal self-discharge is often mistaken for concrete floor causing the battery to drain. Some experts believe that storing batteries on a colder surface might actually slow down the self-discharge (leakage) rate because the floor acts as a heat sink and cools the battery. Large differences in temperature could cause electrolyte stratification within very large batteries (>250 AH) which could accelerate its internal "leakage" or self-discharge if the battery is sitting on an extremely cold concrete, stone or steel floor in a warm room, boat or submarine. Stirrers or bubblers are often used on these types of large batteries to keep the electrolyte from stratifying. Undercharging will also cause electrolyte stratification, which can also result in loss of capacity from sulfation. My point about batteries discharging on a concrete floor was specific to the older style batteries using porous rubber casings: These battery cases were made of porous materials, so storing batteries on concrete floor would accelerate their natural self-discharge due to external leakage. Modern battery cases are made of polypropylene or hard rubber and are better sealed and insulated. We both agree, however, that external leakage-causing discharge is no longer a problem storing batteries on concrete floors, provided the top of the battery is clean and free from wet or dried electrolyte.
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