Hello, More info can be found below.
http://www.apple.com/batteries/ipods.html
Maximum Battery Life
The new iPod touch can play music up to 36 hours, the new iPod nano can play up to 24 hours, the new iPod classic can play up to 36 hours, and the iPod shuffle can play up to 12 hours on a full charge at original capacity. Apple runs tests for battery life using songs encoded at 128-Kbps AAC and songs purchased from the iTunes Music Store (128-Kbps AAC). The songs are played continuously through a playlist without interruption, with backlight and equalizer off. For all iPod models, factory default settings were used except that iPod touch units were associated to a Wi-Fi network and Auto-Brightness was turned off.
Charge Cycles
A properly maintained iPod battery is designed to retain up to 80% of its original capacity at 400 full charge and discharge cycles. You may choose to replace your battery when it no longer holds sufficient charge to meet your needs.
Let It Breathe
Charging your iPod, iPod nano or iPod shuffle while in certain carrying cases 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.