RG,
I have a dual battery system which allows the use of one or both batteries. With it I can also turn off all power which is added safety when the boat is not in use. Of course you do have to remember to turn it off/on

. It was not expensive to install except for the cost of the 2nd battery. My boat yard requires them for all rack stored boats.
I also recommend keeping a jump pack with you being on the island. They are invaluable as has been noted here by others. It can come in handy in the winter too, like when the boy's cars don't start.