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Old 22-07-2021, 09:06   #1
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changing batteries

We have a 58 ft. cruising monohull. It is time to replace all batteries. Currently, we use a combination of 8D 4D and group 31. All are AGM type. Is it possible to replace all with group 31 AGM's. We are older and the group 31's are easier to handle.
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Old 22-07-2021, 09:25   #2
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Re: changing batteries

If you have 8d battery boxes. You can fit three group 27’s in each one. North Star Actully makes a kit.

31’s you’ll need to remove / redo the boxes.
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Old 22-07-2021, 09:55   #3
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Re: changing batteries

We are fortunate to be able to use our 4/1 man overboard retrieval tackle to lift and replace batteries. Even if you hire young strong backs are they careful with heavy acid laden loads.
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Old 22-07-2021, 13:54   #4
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Re: changing batteries

There are always pluses and minuses to every choice.

I am not sure why you have different sized batteries, but it is generally considered to be much better for the lifespan of the bank if they are all the same, size, age, brand, etc.

Certainly the G31 batteries will be smaller and easier to handle. The downside is you will need more batteries, to get the same capacity, which means more individual cells, which means an increased chance of one bad cell damaging the whole string. If you know how to watch for this, it's not a deal killer.

We run our 52 foot boat on eight G31 batteries configured as a 460 A-hr/24V bank. I know of others who run 12 batteries in a single 650 A-hr/24V bank.

So yes, you can.
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Old 22-07-2021, 15:16   #5
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Re: changing batteries

Of course there is the potential problems with the additional jumpers required between the G31 batteries which you will need to manage.
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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Old 29-07-2021, 10:53   #6
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Re: changing batteries

Originally Posted by smac999 View Post
If you have 8d battery boxes. You can fit three group 27’s in each one. North Star Actully makes a kit.

31’s you’ll need to remove / redo the boxes.
If you were going with lead acid batteries they should be mounted perpendicular to the boat centerline. So unless the 8D is incorrectly mounted, putting lead acid GR 27s in the same box would cause them to be in line with the centerline. This would cause incomplete plate coverage as the boat planes. Not sure what happens on a sailboat that heels. I just went through having some pretty severe battery overheating with LA batteries mounted in line with the centerline and very little space between them. I don't know if that was a contributing factor or not, but since I changed them, all has been good. Since you are going AGM it may not be an issue unless there is spacing requirement.
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Old 07-08-2021, 11:09   #7
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Re: changing batteries

I use Dyno 8d batteries because they last about 10 years with care. I'm 74 and hire a couple young gorillas (or is it guerrillas) to change out (every ten years).
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