The CBP-N2 Compact Battery Pack for Nikon SB-900 & SB-910 Flash from Bolt will boost the number of flashes and the recycle time of your Nikon SB-900 or SB-910 flash units. The CBP-N2 can operate on 4 or 8 AA batteries--alkaline, lithium or nickel-hydride (Ni-MH). Lights on the pack indicate Standby, Recycle, or Low Power mode. A thermal protection switch prevents overheating. The CBP-N2 can provide up to 577 flashes per charge, and recycle times as fast as 1.92 seconds. The pack, which weights just 7 oz without the batteries, can also be attached to the bottom of your camera using the tripod socket.