I have never thought about needing a backup battery. Has there been a lot of people needing to replace their battery? So far, my battery seems to be lasting a week or more. Also, I know that in the past it was always advised to let a battery run all the way down before charging the first 2 or 3 times. Batteries don't seem to need that now. Also, if you have a backup battery and never use it will that harm it or should you trade them every once in a while?