I've had pretty much the same experience as the other guys from AZ. The excessive heat kills regular batteries in 2 years, or less. The Optima's (Costco) last about 4 years. On my '91. 5 W-250, I've noticed that the Optima's start to "fade" when they get older. They don't seem to just "drop dead". They give You a little warning that they are going to expire. The truck starter motor doesn't spin as fast.
Something I've wanted to ask, here, for awhile, now. My '03 batteries look like regular batteries but the caps say they are sealed and not to try to pry off the caps, to add water. Have any of You added water to them? My '91. 5's original battery said the same thing, but underneath the label were 6, flush mounted, caps where You could add water. When I finally discovered this, the water level was barely over the tops of the plates. Seems like Dodge wanted us to have premature dead batteries so they could sell more new ones. Joe F. (Buffalo)
I'm amazed the guy with the For got 8 years out of his Optima. Although, I heard of one guy that got 11 years, out of one. He even moved the battery from one vehicle to another!