If you bought the Premium Xbox 360, or have a wireless controller, and dont want to be throwing batterys away every fifteen minutes, you need this.
Theres no two ways about it, Rechardgable AA Batterys dont last nearly as long, and theres no telling when they will run out.
Using this battery pack allows you to see how much energy is left in the battery while in the guide blade during a game, as well as a half way warning, which will increase in frequency until it runs out. (These warnings dont disturb you, the ring of light just flashes alternatly)
The only problem is, there is no need for it to be expensive, and a charger cable needs to be bought seperatly. At least its a one time purchase.