The Wii U GamePad will remain charged for 3-5 hours.
Actual battery life depends on the screen brightness, the features used (such as the camera and microphone), wireless communication use, ambient temperature, and other factors.
If you are having trouble with battery life, try reducing the screen brightness or using Power-Saving Mode.
From the Wii U Menu, press the HOME Button.
Tap "Controller Settings" on the left.
Tap "Settings" under Wii U GamePad.
Adjust the screen brightness by tapping the + and - icons.
When you are finished, tap "Back" or press the B Button.
Tap "Back" or press the B Button to return to the HOME Menu.
Tap "Close HOME Menu.