An improved D.C. power supply for an emergency locator transmitter ELT mounted on an aircraft that does not require lithium batteries but instead uses conventional alkaline batteries in conjunction with a supercapacitor network to provide a reliable power source even when the ELT that is airborne is subjected to extreme cold temperatures that can affect the alkaline battery operation. Alkaline battery pack with a 12 V output is connected to a supercapacitor network board. The supercapacitors are charged when the ELT is activated ON using the comparator network.