water isn't what damages paint, acid does, the moisture you see on battery tops is acid that has come out of the caps.
it makes the water you use to wash it acidic. if you really must use it then just spray it on the battery and remove with a cloth, do not let it flow.
i am saying this because i have experienced leaving tools near my ups battery, they start rusting in no time.
once i left my hydrometer on the battery top for a couple of days, the places where it was touching the battery had become black,because of the acid