The battery in my Zune was completely shot only lasting maybe 10 mins on a "full" charge. The replacement has only been in a couple weeks and the Zune not heavily used but so far so good. My only gripe would be that it would be nice if it came with instructions. I found a youtube video explaining how to change a 30 gb zune batter but it would have been better to have good instructions included. I was a little impatient and scratched the zune up a little bit around the usb connector port. YOU DON'T PRY FROM THE EDGE OF THE PORT, YOU GET THE SCREW DRIVER UNDER ONE END OF THE PLASTIC COVER FROM DOWN INSIDE THE CONNECTOR AND POP IT UP. Again, I was impatient or I would have gotten this from the youtube video and not scratched my zune.