On 2/12/2018 8:03 AM, Joerg wrote:

snip

Simple: When clicking the light on you must stand over it or near it. It
could, for example, issue three short flashes after turn-on for batt-ok,
two flashes for "enough but not for more than a few hours" and on flash
for "it'll be empty very soon".

That's reasonable for a USB powered light with Li-Ion batteries. For a
device running on AA or AAA batteries, not really, because different
chemistry AA batteries have very different voltages and discharge curves.

Battery voltage for primary D, C, AA, AAA, AAAA cells:
Alkaline-manganese dioxide: 1.5V. Linear voltage degradation
NiMH: 1.2V with almost do voltage degradation until fully discharged.
Primary Lithium (LiFeS2): up to 1.83V, typically 1.7V, discharged
if 1.6V or less. Decreasing voltage during discharge, not quite linear.

I have seen a device where there was a switch to flip for NiMH versus
Alkaline to account for the different voltages in order to provide a
more accurate low battery warning, though no option for LiFeS2.