Apple has created an iPod + iPod mini Lithium-ion battery page that explains how to take care of your batteries and maximize their life and performance. Apple has also posted a page for maximizing the lifespan and battery life of your iBook or PowerBook.
Paying attention to just a few common sense pointers will pay off with a longer battery lifespan and battery life for your iPod. The most important thing is to keep your iPod out of the sun or a hot car (even the glove box). Heat will degrade your battery