Where can I find a cheap Li-ION battery to replace the one in my mp3 player?

Title says it all. I’ve got a Nomad Zen Xtra player from Creative Labs, and the battery’s just gone kaput. It started not being able to handle a charge a few months ago (would only last for three hours; I had to plug it in every single day) and now it just won’t come on at all. These batteries are supposed to last for a year and a half, but I use mine a LOT (hour commute+hourlong walks every day+lots of weekend trips) so I’m not surprised that it’s run out so fast (it’s a little less than a year old). So I looked online for a replacement and they’re all like fifty bucks, which seems exorbitant for a battery considering that I could just as well buy a new iPod shuffle every year, and batteries be damned. So what I want to know is:

  1. How can I be 100% sure it’s the battery? I don’t want to buy a new one and then find out it’s the player that’s defective. Especially since I have had this for less than a year and it should be lasting longer. The player does come on and play when I plug it in, but if there’s issues with the connections between the battery and the player a new battery might not work. I took it to Radio Shack but they said there was no way to tell if the problem was in the battery or the player.

  2. Is there anywhere cheap I can get a new one? The CL site sells them for fifty, but I’m looking for something around thirty. Would rather have new than used, though.

If you had it for less than a year it might still be under warranty. Check with Creative.