I have a 2008 ParCar and use to leave it plugged in all summer using the on board charger. I do have a friend checking them monthly and made sure the proper water level was maintained. This year I added the Battery Minder Maintainer-Desulfator after seeing it recommended on TOTV and talking to a few golfing buddies. Their website,
12v Battery Charger, Battery Desulfator, Battery Maintainer, Charger gives a convincing reasons for it. This unit will charge the batteries (under 12 miles, over that they recommend your carts charger) and maintain them with a 2 volt maintainer. Call Jerry Dillen, their sales rep here TV AT 352-205-0092, as he can explain the product. The batteries will use less water and that is especially good when left for months at a time!