For about $66, Apple will replace your iPod’s battery. Fill out a service request and hand over the money. Or you can google up a battery replacement kit, usually for a lot less money, and install it yourself. MacSales, an online 3rd party vendor, offers a suite of do-it-yourself installation videos on its website. The cheapest batteries I have found are at Hong Kong-based Fifth Unit, starting around $6 plus reasonable shipping. I’ve shopped there several times without incident.
Apple recommendations for extending battery life? Shorten your backlight duration–or turn it off alltogether. Pause your iPod when not in use and use your hold button liberally. Keep your iPod at room temperature. Turn off the Equalizer and play back compressed songs with file sizes less than 9MB each.