Publisher Summary This chapter discusses several types of high-temperature thermally activated primary batteries: calcium anode-based thermal batteries, lithium anode thermal batteries, and lithium alloy thermal batteries. In calcium-calcium chromate thermal batteries the overall reaction for the calcium-calcium chromate system is dependent on the discharge parameters. Thermal batteries are manufactured in a wide range of configurations to suit various types of application. The two principal pyrotechnic heat sources used in thermal batteries are a paper-type composition of zirconium and barium chromate powders supported on inorganic fibers and a pressed tablet made up of iron powder and potassium perchlorate, commonly known as a heat pellet. The zirconium-barium chromate heat paper is manufactured from pyrotechnic-grade zirconium and barium chromate; with a particle size of about 1-10μm. Thermal batteries are initiated by either mechanical action using a percussion-type primer or an electrical pulse to an integral electric match (squib). In lithium anode thermal batteries lithium metal is molten at thermal battery discharge temperatures and is retained on high surface area metals by immersion of the metal matrix in molten lithium to form anodes. Often this structure is contained within a metal cup to prevent leakage during cell operation. Another method is the fabrication of lithium alloy anodes, such as lithium-boron, lithium-aluminium and lithium-silicon, which are solid at battery discharge temperatures and thus offer the possibility of simpler construction.