The easiest method would be to power it through the usb port. You can cut and strip a cable. If the cable doesn't have the traditional red and black for ground you'll need to use a multimeter to get the correct wires and polarity. Every usb I've cut has had red +, black -for what it's worth. Wire up the dc/dc converter, bec, or 5 volt pack to the usb cable end and you're good to go.
The cleanest method would be to do a pinout on the board using a multimeter to trace the positive and negative coming from the usb port. You can solder on your own wires and connector of choice. Unless someone has the exact same board, and you're feeling lucky, trace the usb.
