I have a SparkFun MG2639 cellular shield attached to an Arduino Uno R3. I have had both the cell modem and the GPS unit working when the shield is powered from the Uno. I followed the instructions on SparkFun's site to switch the shield to be powered by battery (cut SJ2, short SJ3) and connected a fully charged Li-ion battery. I measure over 4.1 volts at the battery connection pads on the shield but the power LED isn't on and the shield isn't responding. It looks as though it's not getting any power. I also powered it from my bench supply with 5V and it shows no current draw.

Did I miss something in the conversion instructions?

1 Answer 1


Turns out the soldered short of SJ3 was not complete. After resoldering the shield powers up as expected.

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