
I think it's because the lead gets coated with lead oxide if the battery is
not being charged or discharged. I remember some advice from an ancient car
manual guide my father had, which was to use car batteries to power a garage
clock or something similar when they're not in a car. This is supposed to 
prevent the oxidation but I've no idea if it really works. The concrete floor
connection is a red herring.


This may contribute to discharging but would be reversible.
 

Well, this is off-topic, but back in the days when I used to drive bangers
I never found WD-40 to do anything that wiping with a dry cloth did'nt do.
I think the effectiveness of WD-40 is a myth invented by the guy who owns
the company.
