One of the batteries that Dad worked on back in the 1950's was for the Union Pacific railroad. It was intended to be loaded into an underground vault along the

One of the batteries that Dad worked on back in the 1950's was for the Union Pacific railroad. It was intended to be loaded into an underground vault along the tracks in remote areas, and would provide power to run signals through most of a winter. If modern LED power draw is low enough, and the new thermocouple is efficient enough, they could run the signals off the temperature difference between the mountain air and the temperature of the earth about 10 meters down.