Phottix Premium Series BG-D7100 Battery Grip for Nikon D7100 DSLRs. Has AF/On and AE/On button, power switch, command dials and multifunction controller. The BG-D7000 holds 6 AA batteries in the included tray.  

The BG-D7100 also provides a comfortable vertical grip with an additional shutter release and scroll wheel for easy access to the camera functions when shooting in the vertical orientation. The grip also has a tripod socket