It is no secret that drones have a limited battery life. Flying Batteries is an interesting approach to prolonging drones’ hover time. The idea is to have a drone with a docking platform attached to it. A small quadcopter with a secondary battery and docking legs can attach to the quadcopter to enable power transfer.
As HiPeR Lab explains, this approach can increase flight time without adding unnecessary mass to the quadcopter. More info is available here.