So I picked up this Redtop Optima battery from a friend yesterday for free. He says it was dead and sat around for a year or so, I figured why not take it and see if it will charge... come to find it read 4volts BUT theres a small hole coming from one of the cells.. auto parts store guy said I could try some plastic weld epoxy or jb weld.... So I did the plastic weld epoxy and filled in the hole

Any thoughts whether this battery will blow up or not? Ive read of people doing it with other types of batteries...

Umm. I wouldn't recommend it. The guy at the parts store sounds like a winner. I would definitely recommend a new battery. Free or not, is it worth screwing up your car over?