The SD-9 is an external power source. It can hold up to two sets of four R6/AA-size batteries, ensuring a stable power supply for the SB-900, greatly increasing the number of flashes, and reducing recycling time.
The SD-9 is an external high performance battery pack that shortens recycling time and increases flash capacity.
Operates on four or eight AA Alkaline, Lithium or Ni-MH batteries.
The Speedlight must have batteries in place for the SD-9 to operate.