MacUser UK has posted instructions and illustrations on how to replace your iPod’s battery. Both, old and new iPods are represented. Do not use a screw driver to pry off the back of the iPod’s case as instructed by MacUser. To avoid damage to the case, use several strong peices of thin plastic, like a guitar pick or similar. Please see the “Can I replace iPod’s battery myself” FAQ for a list of vendors offering replacement batteries and repair services.
How to replace your iPod’s battery