Back in high school (1985) my auto shop teacher told us that over time car batteries die because debris that flaked off the plates eventually got high enough to short out the battery. Today it seems that the more common failure is caused by build up of sulfate on the plates from excessive use. My little GTI didn't use much power so both batteries lasted over 5 years and I'm pretty certain that debris buildup was the cause of the failure.

The original battery died right after AOL installed about 100 rumple strips in front of its building. The vibration surely knocked off some lose crud on the plates and viola, I had to roll start the car after work.

The 2nd battery died shortly after visiting a new shopping center outside of Baltimore where they had a brick-like entrance driveway. The drive vibrated the car pretty badly and sure enough, that afternoon the battery was dead.

I suspect a service to vacuum out the crud in the bottom of the battery would have allowed me to use the battery for another year or more. Although such a service would probably cost as much as a new battery. :-)