Love the idea but knowing manufacture's they will figure out a way to make it only allow official batteries and charge insane amounts for them.
$800 phone, replacement battery $400
Hey, if we can at least take the battery out and put it back in, that will help a lot with phones with flakey power control. I had a nice phone I had to stop using because sometimes the power management would stop working, and you couldn't turn it on until you let the battery run all the way down, and it doesn't use much battery when the phone is pretty much off.