Somehow managed to fit a 10,000mAh battery inside of my Wii U game pad! Battery life from around 2 hours to (so far) more than 13 hours at full brightness. See captions,
Amazon.com: 3.7V 1500mAh Battery Pack for Nintendo Wii U Gamepad WUP-012, WUP-010 : Video Games
Was the Wii U GamePad's Short Battery Life Planned? — The Indy Gamer
Amazon.com: UCEC Wii U Gamepad Battery, Wii U Accessories 3600 mAh Wii U Battery Replacement Rechargeable Battery Pack Compatible for Nintendo Wii U Gamepad : Video Games
Hands on: Official higher capacity Wii U GamePad battery and Wii Remote Quick Charge Set - Vooks
New Wii U Gamepad Battery Lasts A Definitive 5 To 8 Hours - My Nintendo News
Batterie pour Nintendo Wii U Gamepad - 3600 mah - WUP-012 - Cdiscount Informatique
Batmax – batterie Rechargeable 3600mAh pour Nintendo Wii U, contrôleur de manette de jeu WUP-012, WUP-010
Amazon.com: Tomee Extended Battery Pack for Wii U Gamepad - Nintendo Wii U : Video Games