Hi michugroove,
There is a way to do this as described in the 1/44 post in the link below. However, you will need to respond to the 31/44 posting.
“https://forum.seeedstudio.com/t/xiao-ble-sense-mbed-2-7-2-battery-charge-and-voltage-monitor-analogread-p0-31-does-not-work/ 266438”
When using A0 to measure battery voltage normally, the following points should be noted
The battery voltage must be divided below VDD,
The reference voltage for the ADC should be the internal reference voltage. (default is VDD)