A battery, comprising: a case having a feedthrough port; a feedthrough assembly disposed in the case and extending into the feedthrough port, the feedthrough assembly including a ferrule having a lumen; an inner conductor disposed within the lumen of the ferrule; an insulating core disposed within the lumen of the ferrule and separating the inner conductor from the ferrule; and feedthrough insulation disposed circumferentially around a portion of the ferrule; a cell stack disposed within the case, the cell stack including an anode having a main anode body and an anode tab projecting from the main anode body; a cathode having a main cathode body and a cathode tab projecting from the main cathode body; and one or more separator layers disposed between the main anode body and the main cathode body and electrically insulating the anode from the cathode; an electrolyte disposed in the case; and an insulating boot formed from a material having a thickness, the insulating boot surrounding the cell stack to electrically insulate the cell stack from the case, the insulating boot having a body and an annular lip projecting outwardly from the body, the lip circumscribing an aperture in the insulating boot, the feedthrough assembly being disposed in the lip so that the lip circumferentially surrounds at least a portion of the feedthrough insulation, the portion of the feedthrough insulation being at least three times the thickness of the material forming the insulating boot. a case having a feedthrough port; a feedthrough assembly disposed in the case and extending into the feedthrough port, the feedthrough assembly including a ferrule having a lumen; an inner conductor disposed within the lumen of the ferrule; an insulating core disposed within the lumen of the ferrule and separating the inner conductor from the ferrule; and feedthrough insulation disposed circumferentially around a portion of the ferrule; a ferrule having a lumen; an inner conductor disposed within the lumen of the ferrule; an insulating core disposed within the lumen of the ferrule and separating the inner conductor from the ferrule; and feedthrough insulation disposed circumferentially around a portion of the ferrule; a cell stack disposed within the case, the cell stack including an anode having a main anode body and an anode tab projecting from the main anode body; a cathode having a main cathode body and a cathode tab projecting from the main cathode body; and one or more separator layers disposed between the main anode body and the main cathode body and electrically insulating the anode from the cathode; an anode having a main anode body and an anode tab projecting from the main anode body; a cathode having a main cathode body and a cathode tab projecting from the main cathode body; and one or more separator layers disposed between the main anode body and the main cathode body and electrically insulating the anode from the cathode; an electrolyte disposed in the case; and an insulating boot formed from a material having a thickness, the insulating boot surrounding the cell stack to electrically insulate the cell stack from the case, the insulating boot having a body and an annular lip projecting outwardly from the body, the lip circumscribing an aperture in the insulating boot, the feedthrough assembly being disposed in the lip so that the lip circumferentially surrounds at least a portion of the feedthrough insulation, the portion of the feedthrough insulation being at least three times the thickness of the material forming the insulating boot.