The sensor module does not output a signal if the power capacitor is empty. As far as I can tell this happens if only a fraction of power is left inside it.

In addition power values below a certain threshold are unable to be requested by an attached power network, in which case the capacitor might have something like 2 RF left, but still won't count as empty.

For the later I'd suggest to add a selector like "below 5%".

by putting any kind of a not gate on it :P

Thank you.

Out of curiosity: how do I use the "over 5%" detection as "below 5%"?

Good Guy Project Red to the rescue. ;)