Maintenance and upkeep sure help get longer battery life, but I'm betting its as much the individual battery as it is the care it has received. I don't do battery tenders, don't want to burn down my garage because of them.
I've had batteries last 13+ years, and I've had a few of them fail in 6 months. I suspect the average battery life here is 7-8 years. I don't think the "newer" batteries (made in the last 10 years) last as long as the older batteries did, but really, I have no way to prove that either way. I have 3 vehicles, as long as all 3 vehicles don't kill a battery the same year, I'm a pretty happy guy. Over the years there used to be some brands of batteries that just didn't hold up well, and I avoided them like a plague. These days, I'm not so sure there is much differences in the battery brands, just some extra cost for some big brand names.
In 1984 I visited a Johnson Controls plant in South Carolina and they produced car batteries. While walking down the assembly lines I saw at least 10 different brands including Die Hard and Insterstate, different cases but the same internals...
