The item you purchased is a Pro Battery Grip for the Canon EOS 20D/30D/40D/50D. It can hold 6 AA batteries or two BP-511A li-ion batteries, doubling the battery capacity of your camera. Vertical shutter release button on the Battery Grip makes shooting with the camera in a vertical position much easier, adding stability to the camera. Beware that the batteries should be put into the magazine before inserting the magazine into the grip!
In this professional edition, it comes with several functional buttons as the flash above showing. It will be much convenient while using. It provides additional shutter release, main dial, AE lock/FE lock and AF point selection controls for easier vertical shooting. Having the same function as Canon BG-E2!
Specification: Compatible with: Canon EOS 20D 30D 40D 50D Dimension: 143x111x76mm Color: Black Contains: Pro Battery Grip for Canon 20D/30D/40D/50D x1 Battery Holder for 6AA batteries x1 User Manual x1 Original Manufactory Package