Wemos Li-ion charging boards

After watching a Ralph Bacon video, I decided to power some of my naked ATmega328 remote sensors with Li-ion cells. So I ordered six 18650 and one Wemos charging board locally. Then I hooked up one of my remote sensors to the 3.3V pins I had soldered on the edge of the board and fired up the sensor. It ran for 3 weeks without problems, until the circuit started acting up.

I decided not to wait for the remaining boards to arrive from China and ordered some more locally. one single cell and two double cell boards. What I thought was a Godsend for remote power was now starting to become a nightmare.

As they all from different manufacturers, that don't provide documentation, I have to assume that they all have internal switches that turn off the unit when the drawn current goes below a certain threshold.

The remote ATmega328 is being put to sleep for 8 seconds, waking up and asking if it has anything to do, if not returns to sleep. This happens 8 times per cycle, so that every 64 seconds a signal is sent back to the receiver. The UV sensor and BME 280 are drawing far less than 1 mA constantly but this may not be enough to keep the power supply on some boards on.

Has anybody else had any experience with these boards?