Publisher Summary This chapter provides an overview of thermally activated batteries. In thermally activated battery height is determined by the power required of the battery. The same power output can be achieved in a number of case diameters, by using different intercell connections to provide the desired voltage-current parameters. A thermal battery is a low-impedance device; much higher currents than indicated are drawn for shorter periods. Catalyst Research Corporation highlighted the current-life parameters for a wide variety of general-purpose thermal batteries. Catalyst Research Corporation supplies fast activation thermal batteries. These are to meet the needs of applications requiring battery power to fire squibs, electric matches, dimple motors, and explosive bolts, after battery activation. Catalyst Research Corporation thermal batteries are capable of operation at temperatures between -54 and +73°C, at accelerations up to 2500 g lateral, under a shock of up to 200 g and vibration of 30 g, and also at spin rates of 400rev/s.