There is no problem to connect a non-charging battery to the VIN and GND pads on the back side of the board, provided that the XIAO_RP2040(without charging capability) is used and is not powered from USB-C.
There is no problem to connect a non-charging battery to the VIN and GND pads on the back side of the board, provided that the XIAO_RP2040(without charging capability) is used and is not powered from USB-C.