
It's NOT the concrete floor that does it. The problem is that lead-acid
cells self discharge over time. Even high quality cells (Gates for instance)
will discharge 50-60% over a 3-5 month period of time. Non-sealed cells
self discharge even faster. If the battery was not completly charged
when left sitting, it probably discharged past the the point where cell
sulfiding occurs, which in many cases means a ruined battery.