Once again, the discrete LM3909 circuitry can blink a blue LED while running a pair of alkaline cells all the way down to about 1 V, with one cell ending at 0.2 V and the other at 0.8 V. They started out discharged to 1.2 V each during their useful life, then blinked for a month; it’s as good a use for dead cells as I can think of.
With another pair of not-dead-yet cells providing 2.4 V, it started up again:
That’s a frame from a short video taken in subdued light, just to show it really does work.
The Smell of Molten Projects in the Morning 