It's small handy USB charger powered by 2 AA Batteries. I've been using a 4AA battery USB charger for years, but after saw this neat smaller and lighter 2AA charger kit that fits neatly inside an Altoids Gum Tin, I knew that I wanted one. The kit is well thought out. The printed circuit board is designed to fit the contours of the Tin container. The circuit board is etched with handy part numbers and markings that make it easy to correctly place the electronic components for soldering in to place. The electronics are necessary to boost the ~3 Volts from the pair of batteries in series up to the required ~5 Volts that USB works with.
Very very nice solution. Much easier to carry around than my old 4 battery charger (plus it looks cute to boot (or is that 'boost' ?))