Issue with trying to run HUZZAH32 from battery

[HarveyFunbucks]

Hello! I have a HUZZAH32 that I'm using as a controller for safety shutoff setup. We're using an ADS1115 to read a flow sensor's value to determine when to turn off a normally open SSR, disconnecting the external power to the rest of the unit. To keep this running while the main unit's power is cut off, we've added a battery to the shutoff setup, and have 5V from the main unit running into the USB pin to charge the battery while the unit is on. There is a built-in timer on power on or reset for the shutoff setup so that the unit can be turned on without this However, I've run into an issue where if the main unit's ground is connected to the ESP32's ground and the main unit is off, then the ESP32 won't power on. This prevents the cutoff setup from being able to turn the unit on on startup. We originally designed it to use a normally closed relay that the ESP32 activates in order to shut the main unit off, but during a fault we realized that the relay has to have its default state as open so that it won't leave the main unit on if the controller setup fails, so while reverting to that would resolve this, I can't for safety reasons. The 5V source is non-isolated, so everything should work normally. Is there a specific reason that this would happen? Any advice would be greatly appreciated, and if I need to clarify anything, please let me know. Thank you!

-Bret

[bidrohini]

Here is a write-up about Adafruit HUZZAH32 - ESP32 Feather's Power Management. Did you check this out?
https://learn.adafruit.com/adafruit-huz ... management

[adafruit_support_mike]

Post a photo showing your hardware and connections and we'll take a look. 800x600 images usually work best.