All Unexpected Maker boards have a 3V3 pin on the header, that works as either an Input or Output, depending on how the board is being powered.
If you have an external 3V3 power source available, you can connect that directly to the 3V3 pin to power your board, so long as it is not getting power from any other source on the board (USB/5V or VBAT).
That mean you cannot connect the USB cable to the board to flash it or get serial output when you also have a 3V3 source connected to the pin. Please be careful.
If you do use an external 3V3 source, it’s always good practice to add a capacitor or 2 to the source just before the pin, as powering the board from the 3V3 pin bypasses a lot of the existing decoupling capacitors already on the board.
You can absolutely NOT connect any voltage higher than 3V3 to the 3V3 pin.
You must also not connect a 3V3 source to the VBAT pin to power your board as the VBAT pin has a charge IC connected to it, that could interfere with the source voltage.
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