You could also use this approach for things like deciding how frequently to sync email/text messages, how often to retry connecting to a tower in an area with low reception, how bright to make the screen, how often to run garbage collection.
"Loss aversion" at its best. I just use my battery how I please, and it usually lasts as long as the computer it powers is useful to me. If it dies, I just buy a new one for $50 or whatever, and then it's brand new.