Nikon EN-EL4a Battery
Compact Lithium-ion power supply for Nikon D2 and D3 (also D300 using MB10 grip & BL-3 battery holder) series D-SLR cameras. Up to 3800 images can be shot on one charge. The EN-EL4a is free from memory effect, so it can be recharged at any time or any level. A microchip built into the battery measures discharge capacity and compares it to the full (maximum) capacity recorded when the battery was last calibrated. To charge the EN-EL4a use the MH-21.