Still Rocking the 5 GB
As a proud owner of the 1st generation ipod, I've had some "fun" working with the battery.
Apple's criteria for establishing predicted battery life is something like:
Turn off all the fancy stuff (EQ, Backlight, etc.) so that you're down to just music.
Pick an album, and set your ipod to repeat albums.
Push play.
If you speak to an apple rep, they will probably recommend that you do this very first. It's a very biased test, because no one uses their ipod like this...but it gives the best seeming results because it plays the entire album from RAM, without accessing the hard drive inside the ipod.
If you run this test (which is posted on the ipod help section of Apple's website, btw. Here:
http://docs.info.apple.com/article.html?artnum=61475) and find that your ipod really only works for 4-5 hrs, then you have a legitimate complaint, worthy of a new or repaired ipod.
Also, upgrading the firmware and restoring your ipod also tend to help...no good reason why...but they do.