ESP32 devkit loosely based on the firebeetle trying to improve on it
Using ESP32-S by AiThinker (same as ESP32-WROOM-32)
Added battery protection which can be enganged to allow using 18650 and other non-protected battery instead of only LiPo
Added fuel gauge (3uA idle power consumption) for improved battery monitoring instead of a simple voltage divider of similar power consumption.
Battery charger is suitable for use with 5V solar panels
With ESP32 powered off, total idle power consumption is around 4-5uA max, with the ESP powered depends on operational mode.
The second board can be used to turn the devkit into an ultra low power IoT device
Its powered by the CR2032 onboard which can last at least 2-3 years and has low battery warning
It allows charging the main battery from up to 24V
Has a humidity/temperature sensor & RTC plus power management circuitry
System power turns on and off using push buttons or sensor interrupts.
I a real life scenario the combo can turn on at a preset time in the future, perform its prescribed task then shut down waiting for either the next programmed wake up or due to a sensor or switch or low battery trigger.