had problems with mine recently and when i got it replaced the guy at the shop told me it was because i'd basically used a crappy off-brand battery as a replacement. i got it at a battery store that said it would work fine, but i guess that brand isn't designed for use in that kind of medical equipment or something. of course, then the one that guy told me to get instead that he said is better costs more, but he said it wouldn't die as soon like that. i don't know if it'll continue being true because i haven't had the new ones long enough, but maybe that is the case.