It's no secret to anyone with a Wii U that the Gamepad's battery life is pretty bad. Actually, it's terrible. I can barely hold a full charge for more than a few hours, which means I have my Gamepad plugged in for most of its use. Nintendo at least acknowledged its terrible battery life by releasing a new high-capacity battery for the Gamepad.
The battery will run you $32, which isn't that terrible of a price really, and it's supposed to allow your Gamepad up to 8 hours of gameplay.
This battery offers up to 8 hours of use and can be easily installed using a screwdriver and included instructions.
Battery Capacity: 2550mAh / 9.2 Wh (offers up to 8 hours of use, compared to 3–5 hours with standard Wii U GamePad Battery) Battery Voltage: 3.6V
Please note: Battery duration is an approximation. It can vary according to the use of the Wii U GamePad, usage of wireless communications, the ambient temperature, and the brightness setting of the screen.
You can buy the high-capacity battery directly from Nintendo at this link. If you're a serious Wii U gamer, you should be adding that to your cart right now. Or you know, have Santa get it for you. You still have a day to get your list in right?