3 years ago I had to change the battery in my Miata, it was 6 or 7 years old, I went with a Mazda replacement (special battery in those little cars, and not cheap). Last year I replaced the battery in my Geo '96 Tracker (bought for the wife to learn to drive a manual), I think that battery was about 5 years old. I also replaced the battery in my wife's 2000 Hyundai Elantra , that battery was 7 years old. Of course these were all maintenance free. Don't replace unless it goes bad. If you are paranoid then remove the battery every 6 months and take it to your local auto parts store, they should test it for free.