The idea sprung from the frustration of keeping track of the charge status of an ever increasing supply of batteries. This simple concept is remarkably useful and easy. One side of the rubber band is printed with "CHARGED" in green and the reverse printed with "DISCHARGED" in red. Simply roll the rubber band over to indicate the current status. Never lose track of your charged packs in the field again. The band also holds the balance adapter for an added benefit, removing the possibility of stray wires hitting your props. 10 Rubber straps are included in each pack.