Powering nRF52 without USB

I’m new to the forum as well as the mechatronics environment, and would like to get some precious advice from the gurus on the forum.

Is there a way to turn on the Seeed Xiao nRF52840 without a USB connection?

I am powering it with a 3.7v Li-Po battery connected to the Bat- and Bat+ terminals.
I’m testing a BLE connection, which seems to work perfectly fine when I have the board powered by a USB connection.

However, when I disconnect the USB(hoping for the BLE to work from the Li-Po battery), the BLE seems to not be functioning.

Any advice or help will be much appreciated.

P.S. I’ve ascertained with a multimeter that the Li-Po battery is indeed powering the board when the USB is disconnected.

Is there a “while(!Serial)” in the sketch?
What is the battery voltage when the USB is disconnected?

hi msfujino,
the voltage across Bat- and Bat+ , currently, is 1v. It seems that I’ve been running it for too long.
Does this mean that if the battery is charged to the necessary voltage level required by whatever I’m doing, the board will run automatically when I disconnect the USB?

while(!Serial) is included as follows.

void setup()

if (!BLE.begin()) {
Serial.println(“failed to initialize BLE”);


void loop()
BLEDevice central = BLE.central();

if (central){


“while(!Serial);” waits for a USB connected serial monitor. If there is no USB connection, it will wait here forever.
The battery is charged when the USB is connected and the charge LED(green) is ON. If it is above 4V without a USB connection, you can assume it is fully charged. However, since the voltage is now only 1V, it is possible that the battery is over discharged and will not recover.

Hi, I was wondering about how the battery becomes overdischarged and won’t recover.
I was aware that the there was a battery management chip(BQ25101) on the board that handles the charging and any other circuitry needed.

Does this mean that the battery management chip has the potential to malfunction or that before connecting the lipo battery, I have to make sure that it is fully or almost fully charged?

The battery management chip detects overcharge but not overdischarge. The countermeasure is to write a sketch that monitors the battery voltage and warns when it falls below, say, 3.3 V, or the simple solution is to use a battery with a protection circuit.

Thank you for everything.