Hello @expjwt

according to the description the M5Atom can be powered from the 12 V.

A DC/DC voltage regulator chip is integrated in the ATOM RS-485, which can directly convert the 12V voltage of RS485 to 5V to supply power for M5ATOM, avoiding the trouble of using a separate power supply.

BTW: The 5 V on the header pin is connected to the 5 V on the Groove port. What voltage do you measure between 5 V and GND on the Groove port?