Curious about the Battery Connection

[aymane-eljerari]

I see that only the BATTERY+ has to be soldered on the back side of the microcontroller. I was wondering why there is no connection to BATTERY-. Is it to avoid short circuiting + and -? I haven't looked at the pcb routing but I assume the XIAO BLE's GND pin on the front side is being used. In that case why not connect battery + to the 3.3V pin on the front side of the microcontroller?

[carrefinho]

Yes, BAT- and GND are the same thing; ideally the cutout could just not expose BAT- to eliminate the possibility of shorting.
BAT+ is connected to battery charger and then 3.3V is regulated from battery voltage by a LDO. Connecting battery (3.7-4.2V ish) to 3.3V will blow up the nRF52840.