I think I had 5 years on my C10 battery and I changed it just because.. Some people have good luck with batteries, some don't. Knock on wood, I've been in the former camp. I don't know why this is. I don't use a charger on my C14 and as long as I run it no less than once a month, I've never had an issue with it. I did replace it early (3 or 4 years) because I was going cross country and didn't want the stress of thinking about it going bad.