@paloma https://forum.pycom.io/topic/3834/lopy4-will-not-boot-via-battery-power-on-expansion-board/3 https://forum.pycom.io/topic/3436/expansion-board-3-0-battery-power-not-enough-juice/13 https://github.com/pycom/pycom-micropython-sigfox/issues/167 It seems connecting P8 to 3V3 solves the issue (or an issue which is similar to yours, at least). Don't ask me why.