What volts can I supply the VBAT pin with?

Thanks for the video - that's really helpful.

So if you write:

setInterval(function() {
  digitalPulse(LED2,1,100);
}, 1000);

to the board, then type save() on the left hand side, what happens when you plug the board in to power supply without USB? Does the green LED keep blinking once a second?

I'm just wondering if this could be some kind of strange grounding issue (as maybe both the laptop and power supply are powered off the mains)... I've got a Pico doing plant watering that I left connected to a car battery (so 13v-ish) all summer, and I never had issues even when plugging in a laptop.

Other thing is - did you do the Pico FET tutorial? Any chance you left the solder jumper on the back soldered up? Even if not, if you have some contact cleaning fluid (isopropyl alcohol?) you could rub over the rear of the board, making sure the two solder jumpers are cleaned.

Potentially some salt from fingers could have got on it, and that might be causing problems for the Pico.