I am not sure if your coach has the same thing that my Scenic Cruiser has, but what I was refering to is on my coach there is a Heart Interface panel with all kinds of interesting little lights. On this panel you have all the controls for your invertor/charger. You have a switch to Equalize your batteries. It also shows how many amps the charger is putting into the house batteries. It also shows if you have a fault on the house batteries. But it also has a control that you have to set on what ever shore power you are hookup to. Which could be anything from fifty amp to five amp. But after rereading your post, I am not sure if the Sun Voyager has this system or not. But you should still check the batteries with a hydrometer. It will tell you if you have any dead cells. If the batteries check out OK with the hydrometer, then you have a problem with what you call the brain. Apparently it is not cutting in the charger when the batteries read low.