Since it is a church van it has many drivers and is sometimes taken home overnight by said drivers. I myself have no way of knowing what caused the initial discharge but I know the battery was only 2 years old.
I read up on what could have caused the reversed polarity. Some of the causes are, from jumping a dead battery, recharging a dead battery incorrectly, warped plates in the battery itself.
As for battery itself, it has been exchanged for the new one by one of the other church members who has a church credit card. I believe they get a special discount and don't have to pay tax?