@shicks I agree it would be good to see the software. For my systems I look to have it last 14days before it reaches 3.8V and it is a difficult target unless its being tested for and the time taken on the radio is also characterized.
I see the issue is how to keep the sensor readings delivered reliably while there is enough power, and then when there isn’t enough power to manage the processor reliably until there is enough power – usually when harvested from solar.
I wonder what you see as a valid range for the Vbat, – some readings in the “Unmanaged Power Demand” indicate 5.1V and 3.0V. Can they be valid? For the recommended Adafruit 4.4Ahr battery, with a cellular comms SIM708, what thresholds do you see should be used?
This was what I used to guide my algorithms to avoid resets https://github.com/EnviroDIY/EnviroDIY_Mayfly_Logger/issues/32#issuecomment-959807618
and of course I implement the reliable software delivery