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. Option to use 4 or 8 AA batteries at a time Built-in thermal protection switch to automatically prevent overheating. Recycles as fast as 1.92 seconds (with 4x AA alkaline batteries in flash unit and 8 2400 mAh Ni-MH batteries in Compact Battery Pack). Up to 577 flashes per charge at full power with a Nikon SB-900 or SB-910 Speedlight (with 4x AA alkaline batteries in flash unit and 8 2400 mAh Ni-MH batteries in Compact Battery Pack). Operating Temperature: -4°F-104°F (-20°C-40°C) Operating Humidity: 85% or less Dimensions: 6.7 x 2.8 x 1.0" (17 x 7.25 x 2.5 cm) Weight: 7 oz (200 g)