Improving the battery voltage-to-percentage conversion is on my to-do list, but I need to finish my TRV project first. After that, I can revisit this topic. The idea was to implement a better linearisation algorithm. Currently, the range is 2.5V...3.0V for the Aqara motion sensors and 2.85V..3.0V for FP300. Perhaps the lower threshold of 2.5V is too low; I can use the 2.85V minimum for all Aqara sensors.
After working reliably for several years, two of my RTCGQ01LM started to disconnect from my Zigbee network in the past few months .. 
The last battery voltages reported are 3.015 and 3.065. I think the battery voltage is not the problem in my case. I can prove this by moving these two motion sensors to my Aqara M3 hub and bringing them back in HE via the Matter Bridge.. I can do this quickly this weekend.
