During the last few weeks I've noticed that the JK will be a little slow to crank but will start. Once in a while, a stumble at idle and other small but noticeable things were happening. Saturday I mentioned to my wife that I was going to stop and buy a new battery as I thought mine, new in 07, may be ready to fail. Saturday morning on the way to buy that new battery we stopped for breakfast. Coming back out to the JK, I gave the key a twist, engine cranked slow but started, threw a check engine light and off we went. One more stop, tried to refire the mighty v6 but it was no more. The battery could still roll up and down a window but didn't have enough juice for a start. I think I got pretty good life out of it. Almost 4 years and 67k miles.
Never had a battery last LESS than six years. Same holds true in my boat. People buy trickle chargers, battery tenders, solar cells etc. Store them indoors in winter, facing the sun, on wooden blocks, using only the tears of children to top them off....and I've just run 'em like I run 'em, let the alternator do its job, and the things seem to last 'forever'. Maybe I'm just lucky. Or dumb. Or both