If you mean a xbox 360 wireless controller, then it's where the batteries go.
The best type of batteries for an Xbox controller are the nickel cadmium Duracell batteries, unless you get a SIXAXIS controller, which has lithium ion built into the controller.
The batteries in an Xbox 360 controller are rechargeable. When full charged, they will last several days. The batteries themselves are meant to last the life of the controller.
Change the batteries in your wireless controller.
To recharge your xbox 360 wireless controller you need to buy a play and charge kit(highly recomended) then plug it into the front of the controller and into one of the controller ports then turn on your console and play while it charges.
With a charging dock.
Yes, I Use Rechargable Ones :0
AA, or you can buy controller with a battery pack so you just charge it from Xbox and don't have to worry about buying batteries all the time
The play and charge kit eliminates the need for replacing/recharging batteries. The play and charge kit allows the user to recharge the Xbox 360 controller while playing video games. Allowing continuous wireless gaming.
The Xbox 360 wireless headset automatically charges through the USB on your 360 weather it's on or not. The play-and-charge kit for your wireless controller, however, only charges while the Xbox is on.
There are both wired controllers and wireless controllers. The wireless controllers allow you to be farther away from the Xbox and they also have a dock for recharging your batteries.
Yes, if it discharges, you need new batteries, open the back cover and put in AA batteries, you can also get a wire (Note: The Xbox 360 core (discontinued), has a wired controller)