Abstract: An improved multicell battery of the type heated to an operating temperature and having a plurality of battery cells stacked in series. Each cell having an anode and a cathode which are separated from one another by a separator. Both the anode and the cathode contain an electrolyte that is liquid at the operating temperature. The improvements include providing a pyrotechnic heat source around the outer periphery of each cell. Insulation is preferably provided around the cells. The preferred insulations are compressed foil and peg foil. The separators are preferably made of aluminum nitride. Cobalt disulfide is the preferred cathode material.