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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.
@Kim
No problem. Mind you, I'm a newbie as well and just learning as I go along. So far though it seems that the Espruino boards are very robust, so I wouldn't worry too much about toasting them ;).
Can I connect a battery to VBAT/GND?
Definitely, I just did it with a 9V battery.
Can I connect the batteries to VBAT/GND while USB is connected to my PC?
It seems like you can. In your previous circuit this was not the case and I can verify that the behaviour is unexpected. It also seems to be dependent on whether that pin is a 3.3V pin or not (which is kind of expected). I have a circuit, much like your previous one, up and running with a LED. It works fine when only connected to the battery (light goes on and off), but when also plugged into USB the light just goes from very bright to slightly less bright. Using the same wiring as when the USB is not connected, while the USB is connected, seems to provide the expected behaviour. This is exactly what you are suggesting and my board hasn't blown up just yet ;)