In the event that your iPad battery no longer holds a charge, Apple will replace your iPad for a service fee. The total charge is $105.95 per unit and service takes about a week.
Apple is not actually replacing the battery on your iPad, they are replacing your iPad entirely. You must back up all of your data using iTunes or everything will be lost.
As with other Apple mobile devices the battery is sealed inside the iPad and is not user serviceable. Apple will not replace your iPad if the battery is damaged in an accident or due to unauthorized service or disassembly.
The iPad battery is intended to last 10 hours while surfing the web on Wi-Fi, watching video, or listening to music.