Embodiments herein describe mitigating flexible modes in an airframe of an aircraft by operating a battery for the aircraft as a tuned mass damper. One embodiment comprises an Unmanned Aerial Vehicle (UAV). The UAV includes a flexible airframe, a plurality of propulsors coupled to the flexible airframe that generate thrust for the UAV, a battery that provides electrical power for the plurality of propulsors, and a suspension system that suspends the battery from the flexible airframe and operates the mass of the battery as a tuned mass damper to dampen flexible modes generated in the flexible airframe during flight.