A primary reserve thermal battery includes a primarily CFx cathode, a lithium-based anode, and a solid electrolyte between the cathode and the anode. A high heat source positioned proximate the electrolyte is capable upon activation to heat the electrolyte to a temperature below about 250° C., and more precisely to the melting point of the electrolyte. At that point, the electrolyte undergoes rapid melting and becomes highly conductive, whereupon to cause the battery to produce a burst of power for delivery to an external load.