Join Date: Jun 2006
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My studies of this issue boil down to two broad concepts: 1) Knowing how much you need in the way of amps determines not only how much battery capacity you need, but what means of creating it; 2) There is rarely one ideal battery type or configuration that will meet all your needs. Acknowledging this will dictate a certain open-mindedness.
For instance, I like AGMs not so much for the fast charge as for the low discharge rate. Consequently, I like AGMs on the mooring, or when a boat goes out infrequently. The fast-charge aspect is a bonus, as is the ability to find them in unusual, non "cement-block" form factors that can be put on their sides in otherwise unusual spots.
I like 6VDC golf carts for their ruggedness, their world-wide availability and their ease of maintenance in terms of "hydrometer, distilled water, good to go". To my mind, they make a lot of sense for the long-term cruiser leaving the customary Purolator/UPS service areas.
Given that I will likely settle on my passagemaker with a large 6VDC "wet" house bank, a single 12 VDC "wet" or AGM starter battery on an echo charger, and a single big 12 VDC AGM on the rarely used and rapidly charged windlass battery, I'll need a way to monitor, combine, isolate and co-ordinate all that, plus the means to convert variable wind and sun into acceptable charging voltages for the house banks.
Your situation is more simple in some aspects. As Cam points out, you would be best served in a "mostly always on shore power" situation to just buy stock auto batteries and use the savings to better insulate your fridge, to switch to LED nav lights and cabin lights and to put in decent battery monitoring. Beef it up if you are worried about having enough juice to start the engine after three days by all means, but is this truly an issue?