The Sony VG-C2EM Battery Grip is designed to hold 2 NP-FW50 batteries to double your shooting time. The grip uses a battery with lower power first, then switches to one with greater power when the first runs out. Additionally, batteries can be replaced without turning off the camera.
The grip also adds an extra shutter button, front/back control dials and auto exposure lock. All controls are placed appropriately for easy, comfortable access and buttons, dial and battery cover are sealed for dust and moisture protection