If that socket shown in the picture is the discharge port on the battery, you will need to get a matching female plug and build a wire that will connect from there to the thicker red(+ve) and black(-ve) wires on the controller. I believe that is an IEC320 plug. The easiest thing would be to get a power cable which already has the female connector on one end and cut off the other end to wire to your controller. Those cables are fairly common and used as AC power cables..for example from wall to brick for PC charger.

Of course if that is not the discharge port on the battery, ignore all of the above.