I would like to add a battery to my Raspberry Pi 4. I am building a tablet that can be turned on and off by a switch that brings power from the usb port from a power bank to power the pi, can i tie this to one of those solder points or would it be better to use the gpio header pins? Note the battery is connect to the power bank module still and then the leads come of the usb side of the power bank to a switch in turn would power the pi.
You can power any Raspberry Pi via the 5V pins on the pinheader (Pin 2 + 4) or by soldering to the testpads (Tp1/Tp2/Tp3). Be aware that the pinheader is unfused and that you need to provide regulated 5V at up to 3A to the RPi4. You should use minimum 24AWG/0.2mm2, preferably thicker gauge wire, especially if wires are long.
I have soldered wires directly to the bottom of the board under the USB-C connector to connected to an external 5V power supply and it works great.