Even right after charging, my iPod would die after about 15-20 songs on a nice day. If it was a cold ride, then I may get 5-10 songs. I was searching for a place to have it repaired when my brother told me about this site.
Mine was pretty frustrating, there are so many clips to disengage. Having a sturdy work surface and an extra pair of opening tools made all the difference. I used them to hold things pen while i rotated my iPod to get a better look at the clips. Doing it with the putty knife was not as effective, it was just too hard to see around. The putty knife is the more effective tool to un-clip the sides, just not easy to see around. Even with several interruptions (I was at work) and a clip on one corner that did not understand who was boss, I had it done within an hour. One of my coworkers saw what I was doing and told me that his battery seemed to be on its way out as well. Using the guide for his model we had his battery out in just a few minutes. Now he is just waiting for his replacement to get here.
With the classic model and the thin battery, understanding how the clips worked and where they are is the key. Pay close attention to the pictures to see where you need to concentrate your effort, just pulling and tugging won't free it up. Also watch how you use the case for leverage, once you have it apart, you can really see how easy it could be to bend the back out of shape.