The power consumption and replenishment on a cruising sailboat is a tough problem. Battery space, location, and charging is a problem. I would like to have one massive battery bank that I can tap in to, but the realitiy is, that I can fit 2 main batteries near the engine, I can fit a couple under the galley sink, a battery in the nav station, one under the head sink, two in the v berth. Cruising consumption may mean 172AH a day for 8 days to get across the Gulf of Mexico. I would use considerably less power at anchor and can catch up on my charging.
Big consumption items are VHF (24ah/day), Autopilot(40ah/day), Fridge(29ah/day), GPS/Chartplotter(17ah/day), Instruments(21ah/day), running lights(12ah/day), and miscellaneous items take up the rest. I have to figure out how to replenish the current used and where to store that current.
A high amp alternator (100A) is the best bang for the buck and I can run the engine for two hours per day to replenish the main batteries. One 500W Wind generator is dedicated to the refrigerator batteries. Solar would be nice in theory, but in reality, the sailboat leans, rolls with swells, has limited deck space, and is almost never in the right position to get full sun. Even in the best conditions, solar would only provide power for 6 hours a day (most of the time less).
Because of the battery location problems I have to deal with, I am adding remote batteries and using the existing low current wiring to charge those batteries. A 14 awg wire can only handle 10A for a distance up to 12 feet. 12 awg to 16 feet. 10 awg to 28 feet. I am limiting my current to correspond to the existing wire.
The way I plan to charge them, is to use a VSR that kicks in when the main battery voltage reaches 13.2v (when the alternator is running of if battery charger is on at dockside). That VSR output is connected to a fuse box. The low current wires to the remote batteries run off that fuse box. When the VSR is off, the remote batteries are isolated from each other.
Example. the VHF uses 24ah a day and a 120ah battery would last only 4 days, unless I add 10ah a day by running the engine/alternator, which would stretch me out to 8 days. Everything counts on me being able to start my engine. If the engine won't start, I would reroute the wind generator from fridge over to main batteries and run only critical components of VHF, Lights, and GPS/Chartplotter.
I am still working out the plan, but I may put optional items only under remote batteries and keep essentials on the main batteries. Optional items are fridge and autopilot (I can steer the sailboat manually if I have to, but 24 hours a day is exhausting). GPS/chartplotter, VHF, Instruments, fresh water pump, bilge pump, head pump, and running lights are essentials. The windlass is only used occasionally and while the engine is running. By offloading the fridge and autopilot to remote batteries, I would only use 100ah a day off main batteries and the alternator would keep that working. It is possible to get the 70ah a day for optional equipment from the wind generator, and that battery bank could run the fridge and autopilot and supplemented by the current from the VSR. I could put a remote battery in the nav station, under a battery selector switch, which would be a backup battery to be used in an emergency. Still analyzing, testing, and deciding where best to put my money to work.