Have you connected the GND wires together on all the boards? That's usually the #1 issue for things like this that change when you apply external power
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Have you connected the
GND
wires together on all the boards? That's usually the #1 issue for things like this that change when you apply external power