I work at autozone, and we've got a "used" 51 series battery. Used in our system means its sat on the shelf too long. They sell them for 45 bucks, no warranty. I'm thinking about picking it up and sticking it on the shelf, since mine is going on 2.5 years old. How long will they last? Should I get a tender? Is it worth it? (It'll be 36 for me, I get a 20 percent discount.) Will it live long enough for me to get use out of it?