You can add this to the rumor mill if you want, but according to both Amazon and Gamestop’s websites, the Wii U Pro Controller will apparently have 80 hours of battery life on a single charge. In addition, if we’re to believe both sites, the controller will not be backward compatible with Wii games.
Both sites have the identical description, which states:
Your games, your way. However you think of your gaming style-hardcore, old school, or purely nostalgic-the Wii U Pro Controller puts you in the game. Designed for accessibility and extended gameplay comfort, the Wii U Pro Controller features the dual analog sticks and ergonomic button layout that you’ve come to expect, as well as a rechargeable battery that can last up to 80 hours on a single charge. The Wii U Pro Controller can be used for playing a variety of games-from packaged games at retail to downloadable games from the Nintendo eShop. Look on the back of Wii U game packaging to see which games use the Wii U Pro Controller. Not compatible with the Wii system or games.
Nintendo hasn’t specifically released this information but don’t be surprised if this description is accurate.