hmm, thats interesting. So I guess I use a MOSFET to be safe both ways (when powered or not)?

When the device is not powered the only connection to ESP is +BAT to the A0 pin of ESP32 (and common ground). The battery powers another clock like chip with minute draw.

I have the following circuit which seems to work. My question is whats the resistive load/drain on the battery, if any, that I should consider using mofsets and resistors so they battery lasts a long time. +BAT -> A0 of ESP32. Common Grounds. const int analogPin = A0; void setup() { Serial.begin(115...