my manker e21 have a feature that when it is charging, it won’t light up, but if you disconnect the supply( power down), it will auto start at lowest mode
Interesting idea. Seems to me a light with a charging cutoff at full charge and re charge when the cell drops below a preset voltage due to discharge as a nightlight and sensing where the light illuminates if charging source voltage drops out might be a marketable item. I had something similar that would turn on at power outage or when unplugged but it was rectangular, not hand-friendly, and failed in just a few years.