I saw this while reading IGN's article last night. He said <3 hours for extensive use and <5 hours for non extensive use. So if you are playing ZombiU and have to use the game pad at all times, you can probably only play for about 3 hours, assuming you have it at 100% charge. The game pad always takes 2.5 hours to get a full charge.
However, the Pro controller has an 80 hour charge...Which probably means ~30-40 hours.
I think this is going to cause problems.