Abstract: This disclosure provides systems, methods and apparatus for a combined battery/capacitor energy storage device. In one aspect, the device includes a housing with an integrated battery housing portion, a capacitor housing portion, and a housing lid. A plurality of battery electrodes and electrolyte are contained directly within the integrated battery housing portion and are configured to form an integrated battery within the integrated battery housing portion. The capacitor is connected in parallel with the battery and contained within the capacitor housing portion. A first device terminal and a second device terminal extending through the housing.