I haven't tried myself but I found this at ipodlounge:
"Experienced iPodders will already be aware that the iPod's Achilles heel may be its battery. The battery loses power after a number of charge cycles, yet is not user-replaceable. Previous reports have always suggested that the battery (a 3.7 Volts 1500 mAh Sony UP325385A4H) was manufactured exclusively for Apple, and that it cannot be purchased except through Apple. This would not matter over-much, except that battery replacement requires the iPod to be returned to Apple for repair or replacement, and if your one year warranty is over, this will cost a reported $250 - not far short of the cost of a refurbished iPod. "
here's the link:
http://www.ipodlounge.com/faqs_more.php?id=101_0_10_0_C