Regarding the fact that your son’s watch has 2x the battery life of the others, did you ever test the real capacity of each of the batteries? Speaking from experience, batteries sourced from random Chinese suppliers can have wildly different real-world specs, even within the same lot.
Good to know! I was wondering that as well, but wasn't able to easily swap/test different batteries since I was soldering them to the PCB and then sealing the watch. I'll research how to test capacity across different batteries.
I chart the last 7 days of battery voltage in the companion iOS app, and it does look like they're drawing current differently. My son's watch can sit in deep sleep for days and lose very little charge, unlike the other watches which seem to continue to draw current even though the ESP32-S3 is in deep sleep.
