http://www.ipodbattery.com/
There are other 3rd party solutions as well so
us iPod owners are not at the complete mercy of Apple. But, if the battery is not holding a full charge just before the warranty is up, send it in.
Keep in mind that the iPod batteries are rated for 500 charging cycles. So, if you did a full charge everyday that would equal 18 months. The Apple warranty for iPods is 1 year.