MRK1000 smoking with battery and USB both connected

Hello All,

I'm working on my first Arduino project and this is my first post here. Thanks in advance for your help.

I have an MKR1000 board with a Seesaw I2C Soil Sensor. I have it set up to record moisture and temp to an Adafruit data feed. I have just been testing and developing using USB power at my desk, either directly from the laptop of from my USB hub. I also have used it recently connected to a 5v output Kindle USB charging block. All that worked just fine. Next step for my project is get it running off a battery. I went on Amazon and bought this battery . It seemed to have the right specs from what I've read, 3.7v, 2800mAh, built in protection circuit.

I also have read that the MKR1000 can charge a battery when both battery and USB are connected. But as soon as I plug both USB and battery into the board it immediately gets very hot near the USB connector. I have done this with two different power sources, the aforementioned Kindle charger and USB hub connected to my laptop. With the USB hub it got hot enough that after about 2 seconds the board started smoking. Luckily it does not appear to have done any damage, as the board looks and functions just fine.

Electrical circuitry is far from my forte, so I have no idea what caused this or how to remedy. My best guess is that the battery is causing the board to suddenly draw way more power than normal.

Am I correct that I should be able to have both USB and battery connected to charge the battery? Do I need an external charger for the battery? Could it be that the battery has bad protection circuitry?

Pics of the setup:


Did you check the battery polarity before plugging it in as some have the polarity the wrong way around at the JST connector.


Had a couple with that issue but always check before use.
Swapping the wires over is just a matter of releasing the connector (usually with a pin) and swapping the terminals over.

Seen some people just cut and solder the wires but that is bad practice having red and black connected midway as it could lead to future errors.

Yes both USB and the battery need to be connected to charge.
You mentioned using a USB HUB and they need to have thier own PSU suitable for the max amount of ports on them (500mA per port if all are being used and it is USB 2.0)


the polarity was the problem. Thank you, Bob! I'm relieved that it was something so simple. Swapping the wires around by releasing the tabs on the connector was quick and easy.

Much appreciated!

You are welcome.
Did everything survive ?