I have 6 marine batteries in my house, 4 were purchased last summer and are a part of my solar array, the two from my boat will go into that and two from the array will go onto my boat.
There is plenty batteries in my house:) The problem im having is my boat is only 17 feet, at the rear its about 80 inches wide. On both sides there is boxes with foam. by the transom there is a "bench" where two batteries were located, one for main engine + accessories, other for the trolling motor. Last year my brand new Terrova with GPS got stolen so i removed the trolling battery and stuck my portable gas tank in the spot underneath the "bench".
Now, if i install a second battery, i will have two gas tanks on the floor, one for my main, one for the kicker. Yes, i know i can run both engines out of one tank either by purchasing a tank with two attatchments or by doing a 3 way connection, but still that will leave me with a tank outside. Im just trying to make it work:) Thats the reason why i was asking if i can start my main with a motorcycle battery, or a small car battery.