The MH-21 is designed specifically for the Nikon EN-EL4 battery. The charger has a calibration cycle as well. This 6-hour cycle will recalibrate the battery to spec. This eliminates memory effect and lets the camera accurately display the remaining battery life.
Power Requirements 100-240v AC, 50-60Hz
Dimensions (WxHxD) 4.9" x 2.9" x 1.5"
Weight 8.8 oz (249g)