I just replaced my gamepad battery with an OEM one. The old one only lasted like 20 minutes lol. This new one lasts over 3 hours on a full charge! So Im content with that for now lol

Why did Nintendo decide to put such a small battery in the gamepad anyway? Even my 3DS battery has a larger capacity than the Wii U.

my guess it was to save on price with the intent you will upgrade later. The battery compartment is almost 3 times larger then the provided battery. I bought a 8000mah battery and it fills up most the compartment. The game pad is heavier now but my battery last over 8 hours <3