Sorry to hear of your problem, but you are not the first to do it. Many years ago I came home after a very long graveyard shift very tired and wanted to hook up the batteries in my boat. They hooked up OK and everything was fine until I put the battery selector switch to both and there was a loud pop. I blew the post off the battery and the 80 amp fuse at the alternator. After replacing the battery I did what I should of done to start with, I used some of my red electrical tape and color coded all of my positive wires. My MH is done the same way so there is no confusion on what cables go where. I have not had the problem since.