I don’t want to hijack this thread, but seems like folks thinking about batteries should also think about the whole system and their usage when planning. I didn’t, and there can be a problem with “too much capacity” and too much complexity—and I am thinking—others might go down the same road as I did. I put in two banks of 6V golf cart batteries 20 years ago, a 100 amp alternator, and a smart regulator. I do not believe in starting batteries as they unnecessarily complicate things (another discussion)—if you run things flat or have a bad cell you need only to isolate the cell (use the other bank) and let it recover a few hours to start your small diesel. Theoretically, I have something like 400 ah of storage. I also have a 65W solar panel that is just there to top off the batteries and help out with charging—seems to provide 10 to 15 ah a day, but hard to tell. Here is the problem with this system. I use about 80 amps in a 24 hour period with AB refrig, lights, diesel heater nav gear and radios. Whenever I get around to charging, the smart regulator tapers the charge after time and senses that the bank’s voltage and amps are getting back to 90%+ (I use the two banks together, the only reason to separate them is if I had a bad cell in one bank IMHO). The smart regulator then kicks down to just a few amps of alternator output because it senses “acceptance rate” of your battery bank which is less as the batteries get warmer, increase their voltage feedback, and over total charging time. Result: the system is very kind to the batteries (not heating them up and gassing them by prolonged charging if I am motoring for many hours) but when I am out cruising I am running around with chronically undercharged banks unless I motor for 10 hours (or stop and start the engine so that the smart charger starts its routine with a period of high output again (and then, what is the point of having a smart regulator??). You might gas flooded cell batteries by putting a charge on them faster and have to check the fluid more often, but the option is having chronically undercharged batteries. My system worked fine when I was cruising Central America and hanging out in anchorages for a few days and running the banks down to 50%-60% and then motoring for many hours in calm conditions (cruisers who actually go places motor more than they will admit), but I don’t do that anymore. Now, I go out for a week or two and generally move daily to a new anchorage (with some motoring just to pick up the gear and maneuver). And, while I am out, my banks are undercharged because the smart reguator tapers the charge based on time and voltage feedback from the bank . I will put out there that my bank is too large for my current useage of the boat and that I would probably be better off with a standard internally regulated alternator and half the capacity in my two banks. My local boat yard manager, Bob Vaughn, agrees. So my point is that most folks seem to 1.) have too large a bank of batteries for the way they use their boats—resulting in chronically undercharged batteries while underway. 2.) smart regulators are great if you are motoring for days at a time, but probably contribute to undercharging if you do not. 3.) I won’t go into the point that the complication of needing and wiring starting batteries is an old idea that has been kept alive by folks selling us stuff—even Nigel Calder has come to this conclusion—though he makes his living writing books about complicated systems. In fact, I think we get sold an incredible amount of “more capacity and more complication is better” despite the fact that some of it just makes us spend more time and much more money working on stuff than enjoying sailing. I could have earned a very good living fixing other cruisers’ complicated systems during the years in Central America—it always seemed that cruisers with complicated systems were always down and looking for technical help in exotic placs, but the guys with surfboards and simple systems were doing something else. Now that I am a seasonal, weekly and weekend cruiser, it seems many of my fellow sailors are victims of the marketers of “more is better”. Installing a battery monitoring system was the data that brought me these realizations. Before I had data and facts, I was a victim of the sales folks as well. Just a cautionary note. The magazines and folks at the marine stores and the guys who make a living installing and fixing are not necessarily thinking through your needs. FWIW.
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