DSTE Replacement BL-3 Battery Chamber Cover For Nikon EN-EL4 EN-EL4a Li-ion Battery D300 D300S D700 D900 Camera MB-D10 MB-40 Grip Replacement battery chamber cover for the Nikon EN-EL4 EN-EL4A rechargeable battery Required when battery is teamed with MB-40 or MB-D10 battery pack Cover replaces standard tray that comes supplied with battery pack. Protects the battery chamber when using an external power supply compact and light weight