i'm getting like a bunch of ups type batts rated at 12volt 75 ah. they are about the size of a d3100 and are heavy. they ones i got so far a resting around 12.7 volts. yes they are used. question since i have always used optimas and could get them checked at the local auto parts store, can these be checked there also? if not how can i tell the good one's from the bad?