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The 5V pin is connected the Vin solder pad internally, so the 5V pin can be used to power the seeeduino. However, a diode should be placed on the Vin to make sure connecting a usb port to the seeeduino won’t send current into the battery. This diode should work. The forward voltage drop should be fine since the seeeduino can run on 3.3V. The average operating current is 14.5mA but looking at the datasheet of the chip inside, SAM D21/DA1 Family Data Sheet (microchip.com), the maximum draw could be up to 96 mA. For a good safety factor, I’ll make sure the diode can handle 200mA.
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