On 14/01/2021 10:18, Ahem A Rivet's Shot wrote:
> 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.
>
It's slightly simpler and more efficient to use a step down from two cells.

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