The Precision BG-C3 is a battery grip designed for use specifically with the Canon 20D, 30D, 40D, and 50D digital SLR cameras. It accepts up to 2 BP-511A batteries to effectively double the camera's battery life. The included AA battery holder allows you to use 6 AA batteries for added convenience. The BG-C3 offers an alternate shutter release button, AF point selection, AE lock/FE lock button, and main dial to facilitate shooting in a vertical orientation.