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Old 11-01-2017, 02:23 PM   #1
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Fading 6v wet-cell house bank (880 Ah) : replace with 12v AGM. Any downsides?

It's that time of the decade again.....bite the bullet, and swap out. I've seen some 'physically blemished' 12v AGM batteries, each 174 Ah, on special, at not much more than new 6v USB units.

Space, access and weight are not problematic factors.

Does anyone see any downside to my plan?
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Old 11-01-2017, 02:50 PM   #2
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What would you be expecting to gain from AGMs or from 12Vs?

AGMs apparently want to be recharged to 100% as soon as possible after a discharge cycle. Your experience might depends on whether your normal boat usage permits that.

It would take five 174-Ah batteries to approximate your current capacity. FWIW, I've read it's not great to parallel more than 4 batteries in a bank. No clue whether accurate or not.

Not familiar with "6V USB units." USB?

-Chris
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Old 11-01-2017, 02:56 PM   #3
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What would you be expecting to gain from AGMs or from 12Vs?

AGMs apparently want to be recharged to 100% as soon as possible after a discharge cycle. Your experience might depends on whether your normal boat usage permits that.

It would take five 174-Ah batteries to approximate your current capacity. FWIW, I've read it's not great to parallel more than 4 batteries in a bank. No clue whether accurate or not.

Not familiar with "6V USB units." USB?

-Chris


Thanks Chris,

US Battery is the manufacturer of my current bank. I have 750w solar panels, in addition to 1x 90A and 1 x 140A alternator, so I normally get my bank back up to 100% each en if we don't run the engines.
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Old 11-01-2017, 02:59 PM   #4
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Not sure what 12V battery has a 174 AH rating, maybe 4Ds?

But if you compare generic AGM batteries with generic 6V golf cart batteries (which is what you are doing it seems), I don't really see any difference. The AGMs will let you charge faster, but you are not likely to exceed the flooded cell 25% recommendation in any case. AGMs don't require adding water.

But I really, really like the ability to absolutely know the state of charge by using a cheap hydrometer on flooded cell batteries.

So it is a toss up to me and no downsides other than above for the AGMs.

David
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Old 11-01-2017, 04:23 PM   #5
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US Battery is the manufacturer of my current bank.

I have 750w solar panels, in addition to 1x 90A and 1 x 140A alternator, so I normally get my bank back up to 100% each en if we don't run the engines.
Ah.

Well, I generally like AGMs, but their advantages often cost a lot compared to flooded batteries. No service, great! Reduced off-gassing, great! Faster charging, great -- if you can do it! Alternative installation orientation, maybe useful for some but we haven't needed that. $$$ or $$$$$ depending on brand, not as great.

I dunno that just any ol' brand of "deep cycle" 12V AGMs is really going to be a deep cycle battery. (You could compare predicted cycle life for each option...)

Given your existing 6V/880-Ah configuration (4 pairs of GC2, yes?), and assuming you can easily service the things... I think I'd be inclined to stay with your proven set-up. You could change those to AGMs (Lifeline or at least one other 6V AGM maker), but unless service is a pain, can't say as it'd be worth the money. Or if you want even more capacity, maybe L16s would fit in the same space (heavy, though).

Can't say as I'd want to lift any 4Ds or especially 8Ds, so largest we've used are Group 31s... and they were heavy enough. If those 174-Ah things are in the 4D/8D category, I'd put that weight thing down as one of the downsides even though I recognize you said up front that it wouldn't be a problem for you.

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Old 11-01-2017, 06:18 PM   #6
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I went from 12 x 6V wet to 6 x12V AGM. Best thing I ever did. No topping up water, no mess, no off-gassing. Heaven!

The Odyssey PC 1800 12V are 214Ah each, and have really good form factor and weight. A high volume retailer will get you a really good price as well.
http://shop.odysseybattery.com/p/pc1800-ft
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Old 11-01-2017, 07:25 PM   #7
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Thank you, gentlemen.....

I suspect I may have focused on a deal that was just too good to be true..... here is a link to the unit I considered.

https://deepcyclebatterystore.com/co...atteries-sale/
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Old 11-01-2017, 07:33 PM   #8
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Those prices are great, about half of what i have seen elsewhere. But how do you get them from San Diego to the UK?

David
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Old 11-01-2017, 07:33 PM   #9
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Thank you, gentlemen.....

I suspect I may have focused on a deal that was just too good to be true..... here is a link to the unit I considered.

https://deepcyclebatterystore.com/co...atteries-sale/


What do they mean by blemish? Can go from factory error in labelling to totally fried batteries...

L
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Old 11-01-2017, 07:45 PM   #10
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Those prices are great, about half of what i have seen elsewhere. But how do you get them from San Diego to the UK?

David


Hi David,
Content is actually in San Diego right now, en-route from Canada, next stop Sea of Cortez next month.
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Old 11-02-2017, 05:34 PM   #11
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IMO the only good AGMs are Odyssey, Lifeline and Northstar.

But worth the extra $ only where you need the high CAR, or required by the install space

For value per $, robust longevity, can't beat 6V flooded FLAs, especially the Duracell/Deka ones at Sam's Club and Batteries+
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