According to intellitec the 12 V relay is rated at 100 amps. It looks like there is already a manual disconnect in the picture. If you are going to use the relay you will need to the remove cables that are connected to it and connect them to one side of the relay. Buy another cable that is sized to carry the load and connect it to the battery and the other side of the relay. You will need to build the control circuit for the relay. The relay does not draw any power when it is in either open or closed position.
Products - DC Power Management - Battery run down protection - Battery Disconnects 100A-200A
Chuck & Teri, 1999 35 ft. Dolphin 5350, F53 Chassis with tag axle, Chassis build date 1/99 in Mexico, Banks System, Trans Command, Air Lift Air Bags on rear, Koni Shocks, Blue OX TruCenter, TigerTrak track bars front and rear, Roadmaster 1-3/4" rear auxiliary sway bar, 2013 VW Passat TDI SEL Premium, 1994 36 ft. Avion 5th Wheel. FMCA #F430129