An energy storage system comprising: at least one energy storage module adapted to supply electrical energy to a hybrid vehicle, the energy storage module comprising: a primary enclosure; at least one battery array (902, 904) located within the primary enclosure, the battery array (902, 904) having a plurality of battery cells; an energy storage controller module located within the primary enclosure and electrically connected to the battery array (902, 904), the energy storage controller module further connected to a hybrid control module of the hybrid vehicle by a low voltage connecter; a high voltage junction box attached to a first end of the primary enclosure and having a plurality of high voltage connection terminals, the high voltage junction box having a first opening which corresponds to a second opening of the primary enclosure such that the primary enclosure and high voltage junction box define a sealed cavity and wherein at least one of the high voltage connection terminals is configured to receive a high voltage conductor connected between the energy storage module and an inverter of the hybrid vehicle; a service disconnect connected in a current path between the high voltage connection terminals and the at least one battery array (902, 904); a thermal pad disposed between the at least one battery array (902, 904) and an interior surface of the primary enclosure; and a heat sink disposed on an exterior surface of the primary enclosure, the heat sink comprising a plurality of fins. at least one energy storage module adapted to supply electrical energy to a hybrid vehicle, the energy storage module comprising: a primary enclosure; at least one battery array (902, 904) located within the primary enclosure, the battery array (902, 904) having a plurality of battery cells; an energy storage controller module located within the primary enclosure and electrically connected to the battery array (902, 904), the energy storage controller module further connected to a hybrid control module of the hybrid vehicle by a low voltage connecter; a high voltage junction box attached to a first end of the primary enclosure and having a plurality of high voltage connection terminals, the high voltage junction box having a first opening which corresponds to a second opening of the primary enclosure such that the primary enclosure and high voltage junction box define a sealed cavity and wherein at least one of the high voltage connection terminals is configured to receive a high voltage conductor connected between the energy storage module and an inverter of the hybrid vehicle; a service disconnect connected in a current path between the high voltage connection terminals and the at least one battery array (902, 904); a thermal pad disposed between the at least one battery array (902, 904) and an interior surface of the primary enclosure; and a heat sink disposed on an exterior surface of the primary enclosure, the heat sink comprising a plurality of fins. a primary enclosure; at least one battery array (902, 904) located within the primary enclosure, the battery array (902, 904) having a plurality of battery cells; an energy storage controller module located within the primary enclosure and electrically connected to the battery array (902, 904), the energy storage controller module further connected to a hybrid control module of the hybrid vehicle by a low voltage connecter; a high voltage junction box attached to a first end of the primary enclosure and having a plurality of high voltage connection terminals, the high voltage junction box having a first opening which corresponds to a second opening of the primary enclosure such that the primary enclosure and high voltage junction box define a sealed cavity and wherein at least one of the high voltage connection terminals is configured to receive a high voltage conductor connected between the energy storage module and an inverter of the hybrid vehicle; a service disconnect connected in a current path between the high voltage connection terminals and the at least one battery array (902, 904); a thermal pad disposed between the at least one battery array (902, 904) and an interior surface of the primary enclosure; and a heat sink disposed on an exterior surface of the primary enclosure, the heat sink comprising a plurality of fins.