Comment #1 (Posted by Robert Ings
Concrete has 80 times the specific heat capacity of air, therefore, the bottom of the battery cools far more than the top area. Stratification of the electrolyte results from this temperature difference. This creates a charge imbalance on each plate, which causes the battery to self-discharge at much higher rate. Thermally insulate the battery from what ever suface you set it on to prevent discharge due to stratification.