Nikon SD-9 is a high performance battery pack designed for SB-900. The SD-9 is an external power source ensuring steady power for the SB-900. The SD-9 shortens the SB-900's recycling time and increases flash capacity.
The SD-9 requires four or eight AA alkaline, lithium or Ni-MH batteries. The SB-900 must have batteries in place for the SD-9 to function.