The first USB fan system on FISD. I was tired of having to change a battery mid troop, so I've decided to build my own 5v fan cooling system using a rechargeable usb power cell. I trooped for 4 hours with this setup and only used 1/4 of the battery. Flash back to my second troop where I burned through (3) 9v batteries in 3 hours. This will save money big time!!       Parts list:   Power Cell: http://www.amazon.com/Anker-PowerCore-Portable-Ultra-Compact-Fast-Charging-Technology/dp/B0