When the 24 V battery voltage drops below 18 V, this circuit cuts off its discharge. The circuit is from 1968 documentation. It can be adapted to operate with other voltages.
Among the alternative energy sources, one of the most promising is that represented by Astro-Rei....
This circuit is from the 1977 GE semiconductor manual. The components used are uncommon today....
Found in an Electronics World of 1968, this circuit is indicated for applications in photography...