A battery assembly for a medical device includes an elongate cathode, an elongate anode, an electrolyte, and an elongate housing assembly encapsulating the cathode, the anode, and the electrolyte. The battery assembly also includes a first electrode exposed from and electrically insulated from the housing assembly. One of the anode and the cathode is electrically coupled to the first electrode, and the other of the anode and the cathode is electrically coupled to the housing assembly. Respective axes of the cathode and the anode are substantially parallel to an axis of the housing assembly, and the cathode and anode each include a flat portion that face each other.