magent_mx on 13 October 2010
Pretty easy, but the old ones have more small parts especially in the Rs and Ls buttons that can be a pain to reassemble if you aren't careful when opening them up.
The newer ones are easier as less parts are involved.
To replace the battery is just a matter of remove 5 screws holding the back of the controller, the battery is easily accessible after that, just keep the controller facing down when removing the back (analog sticks pointing to floor) and be sure to remove the back of the controller like a clam shell (open from the handles trying to keep the L and R button side together) it's easier
