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Old 03-18-2013, 01:42 PM   #1
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Gel or AGM and bunch of 6v or a few 8d's?

Good day Cat daddies. I am about to buy the house bank batteries. I found a range of batteries from 8D AGM at Oreillies for about $450.00 up to 8D Gel at West Marine for about $900.00. Napa's marine 8D AGM was about $550.00. Does it matter and if it does matter which one what are the important qualities to look for?
Now, a 6V AGM batterie from Sears was has a 210 Ah and is $225.
I am going to run a 24v system so I would need 4 6v to make the 24v but would that equal 840 Ah for $1000.00
The Oreillies would be $900 for the 2 8D AGM.
Can anyone help make some since or have any experience with different setups. Thanks Paul
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Old 03-18-2013, 01:46 PM   #2
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I am going to run a 24v system so I would need 4 6v to make the 24v but would that equal 840 Ah for $1000.00
No, that would be 210 AH at 24volts.
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Old 03-18-2013, 01:57 PM   #3
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If this is for a house bank, 6 volts are a little more wiring but easier on your back and give more flexibility space-wise. If you have some height, consider 6 volt L16 batteries which give almost twice the amp hours in the same footprint.

DC Battery Sales in North Miami is a great source I have used for a variety of needs, as is Battery Sales in the same area. Freight cost probably off sets sales tax, at least it did for me having them shipped to NC. Good prices, good people. I have bought from both and been to both facilities.

DC Battery Specialists - Wholesale Batteries

Wholesale Battery Distributor - Retail Battery Distributor
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Old 03-18-2013, 02:26 PM   #4
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George is right. When you combine in series to boost the voltage, the current (AH) rating remains the same. To make a 840AH 24V bank, you'd need 16 of those 6V AGM batteries at the cost of about $4000!!
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Old 03-18-2013, 03:04 PM   #5
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People need to think of their in-series bank size in watts, V x amp hours, cuts down on the confusion and allows apples to apples comparisons.
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Old 03-21-2013, 10:00 AM   #6
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I've done detailed comparisons of flooded, Gel and AGM batteries. The main advantage of Gel and AGM is their higher charge acceptance (you can charge them faster), higher charge efficiency (they waste less power and heat up less), they are maintenance free and they don't spill or leak acid so they can be shipped wet.

AGM are a significantly better than Gel in charge acceptance and charge efficiency, while Gel are more sensitive to shock and vibration. So the only reason I know to select Gel over AGM is if they are much cheaper.

The ideal battery bank configuration is all batteries in series, none in parallel, and minimum weight per battery (easier to lift and carry). Therefore, 12 single cell 2 volt batteries in series are ideal. Look at Dashew's boats. Although that does require additional interconnect wiring.

For maximum life, batteries should be located in a cool place, not a hot area like the engine room.
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Old 03-21-2013, 10:17 AM   #7
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Portager has said it all.
I would only add that the additional cost of interconnecting 6 volt batteries is offset if you loose a cell somewhere down the line, you only have to replace 3 cells (6v) instead of 6 cells (12v).
and
AGM's don't make economic sense if you don't need the better charge acceptance because you are motoring every day or two, on a dock w/ charger, running generator for some other reason often.
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Old 03-21-2013, 10:23 AM   #8
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I think that gels are more sensitive to charging parameters. While it is OK to charge AGM and wet batteries with similar conditions from an alternator, for example, I do not think you would be able to adequately mix gel and wet or AGM. We have a "smart" regulator that is set to AGM charging that enables alternator charging for both AGM (house) and wet (starter) batts. I am far from being an expert in this stuff, but my electrician seemed quite happy to set the system up this way!!
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Old 03-21-2013, 10:40 AM   #9
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Quote:
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For maximum life, batteries should be located in a cool place, not a hot area like the engine room.
Unfortunately, most of the people that designed our boats either didn't know this or didn't pay any attention to it. That's partially why I stick to the cheap Sam's Club 6V GC batteries. To me, it's not worth it. We just don't anchor nearly as much and don't mind freshening the bank every few years.
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Old 03-21-2013, 11:43 AM   #10
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.............. AGM's don't make economic sense if you don't need the better charge acceptance because you are motoring every day or two, on a dock w/ charger, running generator for some other reason often.
They make sense if your batteries are in a location that makes checking electrolyte levels and adding water difficult. Or if you just don't want to be bothered with battery maintenance.
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Old 03-21-2013, 11:59 AM   #11
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I don't know how big a bank you are planning, but I would try and find a supplier to the golfcart or forklift industry and buy only brand name (not house brand) batteries. But not PREMIUM batteries (if you know the ones I mean) years ago that may have made sense when they would replace one cell for you; but they don't/can't do that any more and that, IMHO, negates the idea of Premium batteries.
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Old 03-21-2013, 12:11 PM   #12
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They make sense if your batteries are in a location that makes checking electrolyte levels and adding water difficult. Or if you just don't want to be bothered with battery maintenance.
That's certainly the case with my boat and with me.
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Old 03-21-2013, 03:17 PM   #13
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Brooks,
I've heard over and over again that Trojan brand batts are the best and I rarely post such a brand biased observation/recommendation.
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Old 03-21-2013, 04:24 PM   #14
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All good information . The cost / benefit between flooded, gel, & AGM needs to be worked out on a case by case basis I think.
I too have had my best luck with Trojan brand.
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Old 03-21-2013, 04:28 PM   #15
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Put 6 Trojan T105s in last year to replace 2 4Ds. So far so good. Will see how they work out over the long term.
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Old 03-21-2013, 09:06 PM   #16
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Quote:
Originally Posted by Brooksie View Post
Portager has said it all.
I would only add that the additional cost of interconnecting 6 volt batteries is offset if you loose a cell somewhere down the line, you only have to replace 3 cells (6v) instead of 6 cells (12v).
and
AGM's don't make economic sense if you don't need the better charge acceptance because you are motoring every day or two, on a dock w/ charger, running generator for some other reason often.
I am sorry to say but this is very wrong, as is portager's premise that series is "better" The big disadvantage of series driven banks is that if one cell goes bad in any battery you must replace all the batteries. Otherwise you will kill them all soon enough by misbalanced charging. Once you have put them into series all you have done is create one big battery. Please read Nigel Calder's "Boat Owners mechanical and Electrical Manual" an essential document, for a fuller explanation than I can give here. My boat has four major series-driven banks, so this is something I have had to pay a lot of attention to.

While I currently have 4 Trojan L16 batteries as my inverter bank, I would not pose them as the "best" flooded cells. That honor goes to Rolls; four of their monster 8v are in my main house bank. The US Battery L16s that preceded the Trojans got badly used and abused by me and finally died after almost 100,000 amp hours got squeezed out of them. I only bought the Trojans because I could get them local at a very good price and I wanted to make the comparison. Too soon to tell. In AGMs it is hard to beat Lifeline, Rolls or Odyssey (who makes the Sears Platimnums, of which I use a Group 31 to start my genset).
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Old 03-21-2013, 11:06 PM   #17
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what kind of charger do you have? AGM batteries require a lower charger voltage then other batteries. I read once that large alternators can over charge AGM batteries.
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Old 03-22-2013, 12:38 AM   #18
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Brooksie says: "The cost / benefit between flooded, gel, & AGM needs to be worked out on a case by case basis I think."

Attached is a recent analysis for my new accessory battery bank.
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Old 03-22-2013, 04:04 AM   #19
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In May I'll have to buy new batteries for the service bank and I'm very confuse which one to buy

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Old 03-22-2013, 07:14 AM   #20
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what kind of charger do you have? AGM batteries require a lower charger voltage then other batteries. I read once that large alternators can over charge AGM batteries.
I don't have a charger or an alternator yet. I am working with an electrician to began the long road to getting the boat wired.
All this information is great. Thanks guys.
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