Maximum iPod Battery Life
A properly maintained iPod battery is designed to retain up to 80% of its original capactiy after 400 full charge and discharge cycles. You may choose replace your battery when it no longer holds sufficient charge to meet your needs.
Charing your iPod
While your are charging your iPod in certain carrying cases, it may generate excess heat, which can affect battery capacity. If you notice your iPod gets hot when you charge it, take it out of its case first.