Joule Thief adjustable from 0.1 to 0.7 volts, part 1
Almost Dead alkaline battery, can get Leds to light for several days,with this joule thief.
Note that the leds are connected between Collektor and Basic. It allows much more light in the LEDs
Normally leds are connected between Collektor and Emiter, it is bad.
This battery delivers most continuous light at 0.4 volts