May 23, 2021But just adding one more battery isn’t going to make a huge difference, so I still suggest wiring a 3 12 volt RV battery set-up in a similar way to the 2 battery method. Best as I can tell, the existing batteries are wired per your 4 12v battery diagram. Thanks again. Reply. Jenni. April 20, 2021 at 9:10 am Related searches for three battery wiring diagram boat battery connections diagramboat battery charging systems diagrams12v battery bank wiring diagramsolar battery wiring diagramboat battery wiring diagram3 battery marine wiring diagramsolar battery connection diagramboat batteries parallel wiring diagram