On 13 Jan 2021 23:37:18 +0000 (GMT)
Theo  wrote:

> Joe  wrote:
> > Lithium cells have a linear-ish discharge curve, from 4.2V down to
> > around 3V. Any sensibly designed lithium battery will cut off its
> > output at the chosen lower bound, because if it completely discharges,
> > it's dead forever. Not a 'steep' decline, a 'fall off the wall' decline.
> >
> > It's a good idea to have some independent means of anticipating this
> > point.
>
> But lithium ion cells don't work for this application.  We need 5V.
> One cell is too little, two cells is too much.

 One cell and a DC-DC converter to give you a regulated supply,
monitor the cell so you can shut down (well) before there's too little to
run the converter.

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