A recent test showed that the new iPad battery continues to charge even when it says its fully charged at 100 percent.
DisplayMate saw that the new iPad continued to draw 10 watts of power for an hour after reaching 100 percent when using the included power adaptor. It may be possible that the iOS battery indicator is reporting a false value.
The new iPad boasts a larger battery life compared to its predecessor in order for it to withstand long use of the Retina Display and 4G LTE connectivity. DisplayMate also concluded that screen brightness plays a vital role in the amount of battery life you can get out of the new iPad, with video playback averaging 11.6 hours if brightness is set at 50 percent.
Source: Slash Gear