Thermal batteries are classified as primary (reserve) batteries due to being single use only. They are extensively used in smart munitions, fuses, torpedoes, acoustic torpedo countermeasure jammers and decoys, artillery munitions, aircraft emergency escape systems and space applications. Thermal batteries are known for their rugged design, capability to withstand and operate under temperature extremes (up to -60/+90 °C) and dynamic environmental conditions such as mechanical shock, angular acceleration and vibration. As well as their mechanical durability, thermal batteries provide high power densities because of their highly conductive molten salt electrolyte, once activated. Before activation, thermal batteries remain completely inert which contributes to their long shelf life of up to 25 years without performance degradation. Preliminary designs of thermal batteries were employed in V2 rockets developed by Germany during the Second World War.

Thermal batteries are activated by mechanical or electrical initiators incorporated into its header. Upon electrical or mechanical input, pyrotechnic pellets inside of thermal batteries receive enough energy from the initiator to sustain burning until it is depleted. Heat generated from pyrotechnic pellets melts the electrolyte pellets between anode and cathode establishing an ionic bridge between them. The activation process takes as short as 100 – 700 milliseconds depending on the battery design. An activated battery can power electronics (i.e. seeker), pyrotechnics (i.e. sequence timer for emergency escape systems) and mechatronics (i.e. wing drive systems) ensuring their operations at the right time with a high level of reliability.