7½ years on my OEM battery
 

Today I replaced the original battery on my '02 Sebring, - build date 12-01. Since this is June of '09, that's 7½ years out of that thing. It had'nt actually died yet, and was still starting the car with no problem but it's a daily driver and I didn't want to get stranded somewhere. I've never gotten that kind of life out of a battery except for a deep cycle battery in the boat that went 14 years, 1990 to 2004. Batteries must be getting better these days.

Nope, you just got lucky on the car battery. My 94 Accord delivered a decent lifespan on it's battery too.

I replaced the battery on my old 04 Dodge Intrepid 2 years ago, so that would be roughly 11 years.
The trick is keeping the battery cooler.
Intrepids have the battery inside the passenger side front fender.

In the security business, I noticed many of the small lead-acid jelly batteries had very long lifetimes. With my own car batteries keeping the battery on constant float-charge
(13.8volt for older wet batteries, 14volt for calcium alloyed) in the same way results in a similar very long lifetime.
Starter and leisure batteries are not quite the same, but same technology. The starter battery has a spongy lead plate to help for starting/cranking current. Its disadvantage is poor resistance to sulphation if left uncharged for long periods. Hence it's always better to use a car regularly for the sake of the battery. If you only use the car once a week or less, keep it on float charge ALL THE TIME if at all possible.
Leisure or "deep-discharge" batteries have a harder lead plate so the battery is poor for starting purposes, but won't sulphate if left partly charged for periods. So one finds these in grandad buggies, golf carts etc. Sulphation is the kiss of death for a lead-acid battery.
There is a new type of lead battery, called the lead-carbon. It is about half the weight of a lead-acid and contains a supercapacitor. It seems these are appearing in cars at 48volt due to the huge cost of the otherwise quite good lithium-ion batteries. E.g. the 400volt battery for the Toyota Prius was £8000. These batteries have to be cooled as they are liable to catch fire otherwise. No such problem with lead-acid and lead-carbon.
If anyone has the latest on lead-carbon, please post!
Leedsman.

I had a deep cycle battery for my boat that would get charged only a few times each season, then was kept in the basement during the winter. It lasted 14 years. Will use of a float charger have any effect in reversing sulfation in an older battery?