Another thread pointed out that lead-acid batteries are symmetrical when uncharged and can be charged with either polarity. However, I am with those who suggest safety glasses and a chain vest for reverse charging a battery that has become sulfated. You might add a rubber suit too. We had a commercial boat years ago and some worker connected a battery in reverse polarity to an existing battery. It almost killed him.
$100 for a new battery is cheaper than the risk of reverse charging on the chance the battery might be returned to service.
John





