The Traxxas series connector doubles your voltage by combining two 7.2 V NiMH batteries in series to unlock the 50+ mph speed potential of your 1/16 scale brushless model. Dual-battery operation requires attention to precautions outlined in the model's owners manual. Follow all precautions to assure peak performance and reliability of your model and batteries. The Traxxas series connector is for use with 2925X 7.2 V NiMH battery packs only.