The ground and voltage wires will be connected directly to the screw block-terminals on the Motor FeatherWing. Using wire cutters, snip off the 2.1mm barrel jack from the 12V battery pack.
Using wire stripper, remove a bit of insulation from the tips of each wire. A helping hand stand can help keep the wires in place while soldering. Tin the ends of the exposed wire by adding a bit of solder. This will help prevent the strands of wire from fraying. Tinned wires will be easier to connect to the screw block terminals on the Motor FeatherWing.