You searched for: “heat activated battery
thermal battery, fused-electrolyte battery, heat-activated battery
1. A combination of thermal cells.
2. A voltage source consisting of a number of bimetallic junctions connected to produce a voltage when heated by a flame.
3. A high-temperature, molten-salt primary battery in which the electrolyte is a solid, non-conducting inorganic salt at ambient temperatures.d

When power is required, an internal pyrotechnic heat source is ignited to melt the solid electrolyte which allows electricity to be generated electrochemically for periods from a few seconds to an hour.

This process is often used for military applications; such as, missiles, torpedoes, and space missions.