Hi Mishko959,
I wrote a proper sketch and tried it, it worked fine on 3.7V battery power.
If you give me your sketch, I can try to run the same configuration with battery voltage check, BMP280 and LEDs at the same time. You can direct mail me instead of posting it.
Battery voltage measurement can be used with A0 with some ingenuity, but I would recommend using A2 which is not a strap pin. Please also refer to the following link.
‘XIAO ESP32C3, unable to upload sketch or re-write bootloader - #18 by msfujino’
The charge current of the nRF52840 is 50mA or 100mA in the configuration, while the charge current of the ESP32C3 is 370mA. The link below has the results of my measurements. However, if there is some kind of overcurrent protection on the battery side, it should be protected. The 8205A you mention seems to have overcharge detection, but G3JS doesn’t have a datasheet so I don’t know if it can be used. I would recommend that you actually measure the charging current.
‘Charging characteristics of XIAO_nRF52840 and XIAO_ESP32C3’