SUPERCAPACITOR BASED ENERGY STORAGE DEVICE

An energy storage device includes a charge storage assembly, an auxiliary storage element, and a charge control circuit. The charge storage assembly includes an array of supercapacitors coupled in series, a plurality of batteries, and a charge retention circuit. Each of the plurality of batteries is electrically coupled to a corresponding supercapacitor in the array of supercapacitors. The charge retention circuit is configured to maintain a charge state of at least one supercapacitor in the array of supercapacitors when the at least one supercapacitor is in an idle state. A charge control circuit is configured to selectively transfer charge between the at least one supercapacitor in the array of supercapacitors and the auxiliary storage element.