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

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

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No, that would be 210 AH at 24volts.

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

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!!

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.

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.

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 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!!

portager said:

For maximum life, batteries should be located in a cool place, not a hot area like the engine room.

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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.

Brooksie said:

.............. 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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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.

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.

rwidman said:

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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That's certainly the case with my boat and with me.

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.

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.

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.

Brooksie said:

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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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).

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.

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.

In May I'll have to buy new batteries for the service bank and I'm very confuse which one to buy

Sergio "Alemao" Sztancsa, Sent from my iPhone using Trawler

h2orescuemedic said:

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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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.

h2orescuemedic said:

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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I don't believe that is true. AGM batteries are installed in boats and vehicles routinely with no change to the alternator or shorepower charger. Gel batteries are the ones that require adjustments.

caltexflanc said:

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. ..............

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I'm not going to argue that series is better or worse than parallel. In a technical sense, series wins out, but both configurations work just fine. You have a valid point about having to replace all the batteries in a series configuration if one fails.

I think a lot of people don't understand the importance of your last sentence "Once you have put them into series all you have done is create one big battery".

A six volt battery is three two volt cells in series. A twelve volt battery is six two volt cells in series. The only difference between two six volt batteries wired in series and a twelve volt battery is that the connection between cells #3 and #4 is external, not internal.

caltexflanc said:

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.

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The reasons that I said series banks are better is;
1 Historically series banks provide a longer service life than parallel or serial/parallel.
2 Serial banks are easier to trouble shoot and maintain.
3 If a single battery fails in a series bank you only need to replace the failed battery.

Although I believe Nigel Calder's "Boat Owners mechanical and Electrical Manual" contains a lot of useful and accurate information it isn't perfect. He made an error on page 21 when he said, "In a series installation, if one battery fails, you have to replace all the batteries." In a series configuration all the batteries receive the same current, therefore charging is inherently balanced. You can only get "misbalanced" charging in parallel or serial/parallel configurations. Therefore, in a series configuration when one battery fails, you only need to replace the failed battery, but the replacement must have identical capacity.

The main disadvantage with a serial bank is when a battery fails you must replace that battery, but with parallel you can disconnect the failed battery and continue to use the remainder of the bank with reduced capacity. If your planning a long passage or a trip to a remote area and you consider your battery bank essential, you may want to carry a spare battery, which is what Steve Dashew does.

The main problem with parallel banks is it is very difficult to diagnose a battery failure and a failed battery can prevent the parallel legs from getting fully recharged and it can discharge the other legs following charging. For these reasons series banks tend to last longer than parallel banks.

So maybe the old '60's setup of 10 , 12V batts in series to create 120V house current and the selection of universal motors, std house lamps, toaster, made sense?

Jay N said:

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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Very interesting, big flooded cell fanclub member here...

Brooksie said:

Very interesting, big flooded cell fanclub member here...

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Why? Is it because they're cheaper to buy?

Why? Is it because they're cheaper to buy?

The biggest advantage of AGM is their more rapid charge rate.

Few folks are willing to spend the $$$$ to be able to bring a 50% SOC set of house batts to 85 or 90% SOC in a short time.

With out 200+ amps of temperature monitoring charge rate aboard , why pay for what cant be used?

I would rather spend the bucks on bigger LA wet batts.

For the truly affluent the newest LI batts can take a huge charge in 15 min , IF you have the charge amps, and $20 Grand for the batts.

FF said:

Why? Is it because they're cheaper to buy?

The biggest advantage of AGM is their more rapid charge rate.

Few folks are willing to spend the $$$$ to be able to bring a 50% SOC set of house batts to 85 or 90% SOC in a short time.

With out 200+ amps of temperature monitoring charge rate aboard , why pay for what cant be used?

I would rather spend the bucks on bigger LA wet batts.

For the truly affluent the newest LI batts can take a huge charge in 15 min , IF you have the charge amps, and $20 Grand for the batts.

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I know all the advantages and disadvantages and agree FF.

Sort of like all the other discussions about everything from anchors to oils.

My best friend has a nearly new $300,000 42 foot Catalina. Everytime he goes to a boat show...new toys and new systems and upgrades...new anchors, Mobil 1, expensive inverters, new genset ,,,etc...etc ...and is chattering away solar and wind power (never married, no kids...). In the 4 years he has owned the boat he has maybe 100 hours and ZERO nights at anchor).

He bought it from the other guy who swore it would be "his last, retirement, cruiser" who took a job in India and never really cruised the boat....and he bought it with every option possible and was adding stuff as he sold it to my friend.

Two guys who "love" gadgets. My buddy doesn't even understand most of how his systems work and certainly not how they work or not together. Yet he is the perfect candidate to "be sold" on anything new.

I see a LOT of boaters who are exactly the same way...maybe for different reasons...but wind up with the same stuff, boating the same ways.

I spend a lot of time sitting down with these types and penciling out the cost advantages of one system over another...then usually lose then trying to explain why the advantage is lost when they don't upgrade something else...but I'm usually wasting my breath as it happens because they LOVE to talk anbout their new XYZ at happy hour....which is usually back at the home dock and not the cruising grounds.

Oh by the way...the $300,000 outfitted to the teeth boat....when we moved it to Charleston...I had to bring MY PLB along as one thing the boat doesn't have is an EPIRB...go figure...

portager said:

The reasons that I said series banks are better is;
1 Historically series banks provide a longer service life than parallel or serial/parallel.
2 Serial banks are easier to trouble shoot and maintain.
3 If a single battery fails in a series bank you only need to replace the failed battery.

Although I believe Nigel Calder's "Boat Owners mechanical and Electrical Manual" contains a lot of useful and accurate information it isn't perfect. He made an error on page 21 when he said, "In a series installation, if one battery fails, you have to replace all the batteries." In a series configuration all the batteries receive the same current, therefore charging is inherently balanced. You can only get "misbalanced" charging in parallel or serial/parallel configurations. Therefore, in a series configuration when one battery fails, you only need to replace the failed battery, but the replacement must have identical capacity.

The main disadvantage with a serial bank is when a battery fails you must replace that battery, but with parallel you can disconnect the failed battery and continue to use the remainder of the bank with reduced capacity. If your planning a long passage or a trip to a remote area and you consider your battery bank essential, you may want to carry a spare battery, which is what Steve Dashew does.

The main problem with parallel banks is it is very difficult to diagnose a battery failure and a failed battery can prevent the parallel legs from getting fully recharged and it can discharge the other legs following charging. For these reasons series banks tend to last longer than parallel banks.

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You are just plain wrong about this. In a parallel bank you can just replace one battery and pretty much get away with it. In a series bank you will only get away with it for a very short time until the other batteries are dead, and the new one is dead too. I suppose if one never leaves the dock or cruises less than an hour or two from a dock, you can get away with this ultimately very expensive practice. Mr Calder is right, I am right, and you are wrong. I suggest you read the first three chapters of his book thoroughly and then maybe you'll "get it". With two 32 volt banks each consisting of four very large and expensive 8v batteries, one 24v inverter bank of 4 large and expensive 6v batteries, and a 24v thruster/wash down pump bank of two 12v 8D batteries, this is no trifling matter to me.

While I agree in principle with FF that wet batteries are a "better buy", The big advantages of AGMs are (1) minimal (no) maintenance enables them to be stuffed into (almost) inaccessible spaces; and (2) if you anchor out a lot for extended periods, they charge faster which translates into less run time on the generator -- less fuel, less wear.