DSTE Replacement EN-EL4 EN-EL4A Battery + BL-3 Battery Chamber Cover For Nikon D300 D300S D700 D900 Camera MB-D10 MB-D40 Grip Replacement battery chamber cover for the Nikon EN-EL4 EN-EL4A rechargeable battery Required when battery is teamed with MB-D10 MB-D40 battery pack The cover only used when the battery is placed in the camera grip Protects the battery chamber when using an external power supply The battery and cover kit can be used perfectly in your camera grip.