The Canon Battery Grip BG-E7 is an optional battery grip designed specifically for the Canon EOS 7D. It allows users to load a choice of one or two LP-E6 battery packs (not included). With two packs, the already impressive battery life is doubled, compared to using a single LP-E6 pack in-camera. This is especially useful when taking advantage of the camera's movie mode or Live View mode - operating modes that use more power. In addition, with the included battery magazine you can alternatively also power the camera off six AA batteries.
Furthermore the BG-E7 provides full vertical shooting controls, which can be independently turned on or off as the photographer needs to enhance camera handling, especially for shooting vertical pictures.