I have a SparkFun Pro nRF52840 Mini and it works well when I power it via USB but when I power it from a 3.7v 500mAh battery it won’t power up and in-fact it starts smoking. I have confirmed that the power from the battery is 3.6v. In addition, this occurring with the board right out of the package (no headers soldered to it, not anything connected to it other than the battery pack). This has happened for the past two SparkFun Pro nRF52840 Mini boards I have ordered. The first one did not power on via the battery (but there was no smoking at least). The second one is the one that is smoking. Did I just randomly get two bad boards with similar battery powering issues? Could it really be the battery causing these issues? Is this a known issue with a batch of these boards? Any help would be appreciated thanks.
Hi nyw,
Check to make sure the polarity of your battery matches the JST connector on the Pro nRF52840. Judging by your description, it sounds like the polarity is reversed on your battery and is damaging the charge and/or power circuit.
Wow that seems to have been it! I get blinking lights now with better power. I am not sure how I got a battery with a reversed polarity JST connector. Hopefully I disconnected everything before I damaged anything. The blinking lights definitely bode well for a working board but I will have to test everything to make sure. I did think polarity could be an issue but discounted it thinking the JST connection was fairly standard.
That’s great to hear it was just an issue of reversed polarity. You’ll find in some RC and drone applications the polarity of a battery is inverted compared to what we carry and the battery circuits we design. Any batteries you get from SparkFun will always have the same polarity as our JST connectors but it’s always a good idea to do a quick check with a multimeter (especially if you pulled a battery from another device or purchased them from another company).
With the board that appears to be functioning normally, most likely everything is okay but I would recommend probing the MCP73831 battery charging IC with your meter to make sure there are no shorts and the charger is working properly. You can refer to the schematic and Eagle files for help identifying pins or the [datasheet will also help to test that component. Hopefully, everything is working okay and shorting the circuit with the reversed battery did no lasting harm.
Let us know if you run into any other issues or have any other questions about the Pro NRF52840 and we would be happy to help as much as we can.](https://cdn.sparkfun.com/assets/learn_tutorials/6/9/5/MCP738312.pdf)