The Phottix PPL-200 Battery Pack is designed for Hot-Shoe Flashed & Studio Lights. With available Nikon or Canon cables this power supply can be used to charge two compatible flashes at the same time. The Ni-H power pack can fire a Nikon SB-900 approximately 1500 times at full power with recharge times of 1.5 seconds. Two SB-900s could be fired 750 times before you ever have to consider running out of juice.