Spektrum Receiver 40000mAh 2S2P 7.4V Li-polymer Battery Pack with Thunder Power Balancing Connector, Rx Lead with Universal Connector and 16 gauge High Power Lead with EC3 Connector. Specifications: Dimensions: 2 1/2" x 2" x 1" (64mm x 49mm x 26mm) Weight: 6 oz. (170g) Voltage/Capacity: 7.4V/4000mAh Configuration: 2 cells in Series, 2 cells in Parallel Always use with Voltage Regulator!!!! Charge only with Li-Polymer Charger!!!!