Vulcan I've spent the last 15 years reading every thing I can from a scholarly dissertation from 1927 to the latest and greatest stuff at Battery University.
Unless the tops of batteries are kept scrupulously clean it may contribute to self discharge.
As cycle life increases self discharge rates increase as a result of antimonyial poisoning of the plates. Flooded deep cycle batteries have more antimony to start with, that is one reason that their self discharge rates are higher than a car jar.
I've managed to get 10 years of life out of Walmart jars under conditions where I draw 275 amps, which most folks don't, so I'm doing a few things right.