The main difference between the regular Wii and the Wii U was that the Wii U came with the new tablet-like GamePad controller. The GamePad has its own screen and allows you to play a separate role in a game that your friend is playing on the TV. What's more, the device is capable of displaying companion content (such as maps, inventory, etc.) for the game you're playing on the big screen. The only issue with a controller with all that extra functionality is that it eats up the battery a lot more quickly than your standard game controller. Users can only expect between three and five hours of play on a single charge.
Nintendo is hoping to combat this problem with a new larger capacity 2,550 mAh GamePad battery. The battery launched in Japan this past summer and now it's headed for Europe. Amazon UK currently has the battery listed for £25. The new battery promises between five and eight hours of play once it's been installed. The unit is also on sale in Germany for €37 (no word on availability for the rest of Europe).