One IMPORTANT thing to remember about a 12Volt deep cycle battery is that a full charge is 12.6Volts and a 12Volt battery that is at its 50% voltage is 12.3Volts, I know that does not sound right, but it is. A DEAD 12Volt battery is right around 10.5Volts. That happens to be "0" Specific Gravity of the battery.

You also need to know how many watts each of your big drain devices use, IE AC, Electric Heater, Microwaves, Hair Dryer… to calculate the Amps that your wires will be carrying. You do not want to start a fire in the boat, or kill your batteries in an hour or two. If Helena's electric cooking pot uses 1,500 watts your wire to the outlet where it is plugged in must be able to carry 12.5 amps. (1,500 watts / 120VAC = 12.5Amps) easy formula to remember, part of Ohm's Law. So for your new AC, it may be rated at 18 amps running (2,160 watts) what is the starting amps as that is when the compressor is just starting up and it will be more than the 18 amps. I was just using these numbers as easy examples. Best to make a list of items and their wattage ratings (usually listed on the item) so that you do not use any combinations that will rapidly drain your battery and the list will give you an idea as to how long you can run it without killing your batteries. I recommend 1/00 copper wire from the batteries to your cut-off switch and to the distribution point (fuse panel), just to be safe.

We have 12 years of Solar RVing and a lot of Dry Camping (no campground electric), Solar/batteries are great if properly maintained and not abused. Like only using the Microwave at high-noon with 100% of sun, absolutely no AC on batteries.

Now you know why my nickname is ElectronicsNut.

Have fun! Wave as you pass Dunedin on your way south.