What I did was drill out the rivets on the trolling motor battery tray and turned it sideways and added another tray next to the one I relocated. If you put the trays as close to the end of the compartment as possible there is enough room to put both trolling motor batteries in the one side and the starter battery on the other side.
I will try to take some pictures of the install if you want me to but I cant do it till this weekend because I am at home in Illinois and the boat is at Ky. lake in Tenn.