Re: 2 Batteries = 12 Volts. How to? Whats the advantage? FUSE? Correct or Not?
(2 12volt batteries together, Goal 12V output) 1). positive terminal to positive terminal 2). negative terminal to negative terminal 3). Positive from one battery out 4). negative from other battery out.
Is this correct?
Do I need Fuses anywhere? If so where and what size? Why?
Will I have Longer life on water?
Don't want to damage electronics??
I will primarily use this for electric motor!
You don't need fuses between the batteries. Dual batteries in parallel provides more capacity for things like trolling motors. You method of connection is correct and will not cause issues so long as one battery does not go bad and drain the other.
That being said lets go to what you actually want to do. If your goal is to run the boat to go fishing and then use it to run trolling motor and fish finder, the you need a 2 battery bank setup. One bank (battery) to use to start the engine, and another used to run the trolling motor and fish finder. This way if you run the trolling motor long enough to drain the battery, you have the other bank to start the engine and get back home.
If your trolling motor is 12V then one additional battery is needed, if it's 24V you need two.
Need more info on how you plan to use your setup