[tentcamper]

Never looked at how the wire from the 7 pin connector is run? Is it run as one group to the power center (converter), or is it one group to the area behind the fridge?

If its behind the fridge? You could just add your wire to the connector that connects the 7-pin battery charge wire as it leaves group of wires, and connects to a wire that heads back to the power center. So you would end up with one wire going to the 7-pin connector, one going back to the power center and the new wire headed to the new battery.