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Marine Battery

Old 03-01-2013, 02:11 PM
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Default Marine Battery

Hey looking for advice on types of battery/s I should get to replace mine. I have a two battery set up with switch. 225 hp motor and all your standard electronics (plotter, radar, sonar, weather, radio. lights ect) looking to spend around 150-200 each

should I get one for starting on "1" and a more house battery for "2" with more AH?
thoughts Group 27's ??
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Old 03-01-2013, 04:58 PM
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Originally Posted by cbass71 View Post
Hey looking for advice on types of battery/s I should get to replace mine. I have a two battery set up with switch. 225 hp motor and all your standard electronics (plotter, radar, sonar, weather, radio. lights ect) looking to spend around 150-200 each
The correct battery choices will depend on several variables that you have not as yet adequately described, most notably including the actual configuration of your electrical system; "two battery set up with switch" is not nearly enough to distinguish between a true two-bank system with segregated "Starting" and "House" loads, or simply alternate batteries of which each power everything when selected. Depending on this question in particular, and how charging current is distributed to these two batteries, you may or may not want to match the basic constructions and chemistries of the two batteries.

Ideally, the Starting battery should be an open-cell flooded type, as these generally permit the largest short-term current capabilities (such as when cranking an engine for a few seconds at a time). But they require diligent ongoing monitoring and maintenance to ensure both their best performance and good life-expectancy.

AGM batteries are much easier to live with, and provide a number of advantages in terms of self-discharge rate, charge-acceptance rate, and deep-discharge tolerance. They are thus ideal for "House" banks; but when carefully chosen, can also work well for engine-starting applications.


should I get one for starting on "1" and a more house battery for "2" with more AH?
"Starting" vs. "Deep Cycle" is yet another issue beyond any questions of basic construction and chemistry. For example, both open-cell flooded batteries and AGM batteries are available in both "Starting" and "Deep Cycle" variants.

As for the capacity requirements... Bigger is always better. And given the assortment of electronics you mention (plus, no doubt, many other things you didn't mention, such as lights, pumps & appliances), I'd want a fairly robust House bank. What do you have now, and how is it working out?


thoughts Group 27's ??
BCI Size Group designations define ONLY the case dimensions, plus certain details such as terminal types/sizes/locations, etc. (cf. http://www.flemingsalesoem.com/fleming/BCIChart.htm); they do not imply ANYTHING about specific capacities or performance capabilities. As such, they are not useful as a "single figure of merit" in selecting replacement batteries. The Owner's Manual for your engines should specify the minimum nominal (20-Hour Rate) capacity, CCA, MCA and Reserve Capacity required; and THAT is the basis upon which you should be making any comparisons.



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Old 03-02-2013, 05:25 AM
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The other key factor is how you use your boat. If you spend time at anchor or otherwise with no charging source going (which we do as long distance cruisers) you'll want to estimate how much current you'll use (in Amp-Hours, or AH) before you crank up the engine again and start recharging. That will help you decide what the capacity (in AH) of your house battery should be - about 3-4X the number of AH you expect to use between recharges.
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