ESP32: RTC memory, the fast persistent storage that survives deep sleep
Use RTC_DATA_ATTR to keep state across deep sleep on the ESP32. Boot counters, last-known sensor values, and the gotcha that it does not survive a power cycle.
Tag
#deep-sleep
2 tutorials
ESP32: deep sleep and battery life, the honest numbers
Put an ESP32 into deep sleep and measure the actual current draw with a multimeter. Includes what to expect on different boards and battery chemistries.