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post #63 of Old 10-01-2008
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Camaraderie - I agree to a point .... that would certainly be better than two "starting" batteries ... but I'd suggest that the optimal setup where space is limited would be two "Dual Purpose" type batteries. That way there would be plenty of CCAs in either batery to start the engine, and nearly as many amp hours in reserve as one would have with a pair of "deep cycles" .... and I believe you'd get more longevity than with a pair of deep cycles which had been subjected to starting use. At least that's what the tech advisors told me at Decca Battery which is located near where I used to live.
I should have mentioned in my post that there is also confusion among many people about what constitutes "different types of battery" when it comes to combining them in one electrical system. This was mentioned briefly in this thread, but it bears underscoring.
It is fine to combine "starting", Dual purpose" and "deep cycle" batteries in one system as long as they are all of the same construction type. By this I mean they should all be "wet cell" types (the typical battery with lead plates suspended in an acid solution and which usually must be topped up with water) OR "AGM" batteries in which the acid is absorbed in glass mats between the plates OR "gel cell" batteries in which the electrolyte is in the form of a gel. The latter two are considerably more expensive to buy, but generally offer more usable power size-for-size, will not spill acid out if overturned (such as in a knockdown or capsize) and last longer with minimal maintenance. Wet cell, AGM and gel batteries should NOT be used in the same system because they have different charging parameters. Because they accept charges at different rates when they are in the same system the probability exists that one type will be under charged while the other will be over charged and ruined.
FWIW, I probably should also have mentioned that I personally am using a Balmar 100 amp alternator fed through a Balmar three-stage "smart regulator" and a battery combiner such as mentioned earlier.

Captain Harry
Life's Short ... Eat Dessert First!
La Nostra - CSY 44
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