Recommended AGM Group 31 Battery

[OldKenT]

Can anyone recommend AGM deep cycle group 31M batteries to power a 24-volt trolling motor?

I need to replace my Sears Platinum batteries (which Sears no longer sells) because one is discharging very quickly.

The specs for my current Sears batteries are the same as for the Odyssey Extreme Series 31M-PC2150 - 205 minutes reserve, 1150 CCA, 100 Ah at 20 hour rate, and 92 Ah at 10 hour rate.

Has anyone here used that Odyssey battery? Or the Odyssey 31M-800 which has 188 minutes reserve, 810 CCA, 99 Ah at 20 hour rate, and 94 Ah at 10 hour rate?

Thanks for your input.

[Jefecinco]

I believe I read on a previous continuouswave thread that the former Sears, Odyssey branded AGM battery is now sold by West Marine in their brand name.

[OldKenT]

Thanks, Butch.
I stopped at a West Marine store today. They have an AGM with good specs (800 CCA, 200 minutes RC, 105 Ah at 20 Ah rate) priced at $309.99 which the clerk said is manufactured by East Penn. The Odyssey Extreme 31M-PC2150, which is identical to the Sears Platinum I used previously, really has an extreme price - $403.36 from Odyssey, whereas the Sears was priced at about $250.
Tough choices.
Would appreciate any experiences others have had with high quality AGM batteries for 24 volt trolling motor setups.
Ken

[jimh]

I believe I read on a previous continuouswave thread that the former Sears, Odyssey branded AGM battery is now sold by West Marine in their brand name.

There was almost universal agreement in c.2011 that the battery being sold by Sears as a Sears-brand DIEHARD Platinum Marine 34M and the battery being sold by Oddysey as the Odyssey Drycell Extreme 34 PC1500MST were extremely similar and that Odyssey was likely the real manufacturer of the two batteries. See the discussion and some evidence of this in

http://continuouswave.com/ubb/Forum6/HTML/002907.html

(I know this present discussion inquires about a different size Odyssey battery, but I the historical article was about the 34M size, which is why I have mentioned that model.)

I don't recall any mention that West Marine was now selling a similar Odyssey-made battery, but that doesn't mean they aren't.

I tried to locate the Sears-brand DIEHARD Platinum Marine 34M AGM battery on the Sears website, but I could not. I think they no longer have those Odyssey-made batteries in the Sears-branded product line.

You can still buy the ODYSSEY Extreme Series Marine Battery Model 34M-PC1500ST from Odyssey for $301.64 via their on-line store. You can buy it from other sources, but the price is not any lower and is actually sometimes higher.

I have two of the Sear-branded (presumed) Odyssey-made AGM batteries on my boat. I believe one was purchased in 2010 and the second a year or two later. They have provided excellent service. I am expectantly hoping they will continue to provide that excellent service this year, too.

I would expect that a different size battery in this same series from Odyssey would provide similar results.

[jimh]

The AGM batteries that WEST MARINE is selling look more like the DEKA-brand DEEP CYCLE INTIMIDATOR®
AGM BATTERIES than any sort of Odyssey battery. They are made in the USA by West Penn. Their specifications look very good, as does the pricing

For a Group 31M battery, the DEKA model would be their 8A31DTM battery, with these parameters:

CCA = 800-Amperes
MCA = 1,000-Amperes

Ampere-hours = 105-Ah at 20-Ampere rate

Reserve capacity = 200-minutes (at what is presumed to be a 25-Ampere load)

Weight = 69-lb

Details: Black cover, gray case; dual-terminal universal design (automotive post and threaded post); has handle; rated non-spillable.

I believe this same battery is being sold under the brand name DURACELL at Sam's Club. My local Sam's Club has the Duracell® AGM Deep Cycle Marine and RV Battery - Group Size 31 for $180. That is really quite a good price. Try this link:

http://www.samsclub.com/sams/marine-batteries/3990113.cp?navAction=pop

[OldKenT]

jimh, Thanks for the information about the DEKA / Duracell batteries. For an AGM with those specs, $180 is indeed a great price. Thanks for the references.
Ken

[jimh]

Ken--no problemo to dig up that information. If I find my six-year-old Sears Platinum AGM is not still working, I'll hunt down one of the DEKA AGM batteries for my own boat. Let me know how it works for you if you get one.

[JRP]

For a Group 31M battery, the DEKA model would be their 8A31DTM battery, with these parameters:

CCA = 800-Amperes
MCA = 1,000-Amperes

Ampere-hours = 105-Ah at 20-Ampere rate

Reserve capacity = 200-minutes (at what is presumed to be a 25-Ampere load)

Weight = 69-lb

Details: Black cover, gray case; dual-terminal universal design (automotive post and threaded post); has handle; rated non-spillable.....

We had a pair of these Deka Goup 31 Intimidator AGM batteries on our previous boat. It was a sailboat stored on a mooring, and it had all the usual domestic electric loads including refrigeration. The batteries did yeoman's work and rarely received as much charging as I would have liked them to receive.

We much prefered to sail, so what minimal charging they received came largely from the engine during brief periods motoring in and out of our marina and occasionally motoring in light air. The engine alternator was a very basic 55 amp Hitachi, with an internal regulator -- no "smart" charging profile or high output from the alternator. They did receive some shore power charging from a "smart" charger when we occasionallly rented a transient slip.

After a dozen+ years of hard use, we replaced them. Not because they had died, but because we were selling the boat and I felt a new owner would want new batteries. So my longevity experiment ended. Of course, they were replaced with the same model, at $189/each.

I would not hesitate to recommend these Deka Group 31 Intimidator AGM batteries or to purchase them again.

[jimh]

JRP--many thanks for adding your narrative and endorsement to the discussion. I find that first-hand experience is often the most valuable data. The DEKA DEEP CYCLE INTIMIDATOR AGM battery looked good on paper, but it looks even better now with the addition of your history with them.

[JRP]

I neglected to mention that during that entire 12-year-or-longer period of ownership, the Deka Group 31 AGM batteries required zero maintenance. They were installed, and then removed 12-years-or-more later when they were replaced. Aside form an annual visual inspection (removing battery box top and eyeballing them), they were never touched. Terminals never required cleaning, and the sealed batteries never required that electrolyte be added or tested.

[JohnW]

Cabella's recently had the Advanced Angler AGM on sale for $50 off and free shipping. I've heard good things about them and picked up a new one for starting. Hasn't come in yet.

[OldKenT]

The DEKA Intimidator Group 31 AGM can be purchased directly from East Penn, which operates regional warehouses and stores in New England, for $294.69. I called and was told each warehouse operates also as a retail store. You can find sellers for your region on the East Penn website.

The Duracell Group 31 AGM, which jimh pointed out is available at Sam's Club for about $180 with a core trade-in (for members), can also be purchased through many others identified on the driveDuracell website. In addition to the list, there is a map of automotive stores in many states. I called Monro Muffler, which connected me to Batteries + Bulbs where it can be purchased for $239.99 without the core trade-in.

But questions are prompted by the advertising: Can one expect that a manufacturer will use the same purity lead plates for each of their labels? And how much might that matter? East Penn makes the Group 31 AGM Intimidator and the like battery for West Marine. What is the view here? Are they building to different specs? For example, Sears always advertised that its Platinum Marine batteries had 99.9% pure lead plates. Presumably, that was a selling point. No one else says that, although Cabelas says its X-900, mentioned by JohnW, has "pure lead plates".

[JRP]

The DEKA Intimidator Group 31 AGM can be purchased directly from East Penn, which operates regional warehouses and stores in New England, for $294.69. ....

That exact battery is available locally to me for $189.95, which is the amount I paid for each of mine. Scroll down to the third battery shown on this page:

http://www.stevensbattery.com/marine-and-rv-batteries.html

[jimh]

The lead purity in a lead-acid battery contributes to the reduction in the self-discharge rate of the battery. Lead is often mixed with other metals in battery construction to increase the strength. In AGM batteries it appears that softer lead can be used because the plates are separated by mat. For that reason, some AGM batteries use very pure lead. Many people have confused themselves into thinking that AGM construction lowers self discharge. It does not. Lead purity lowers self-discharge. If you get an AGM with very pure lead, you get lower self-discharge.

The majority of lead in use now is from recycled lead. Since the lead being recycled is often less-than-99.99-percent pure, the lead from a recycling smelter is not going to be pure lead. (It is possible to recover pure lead by recycling methods, but most re-cyclers can't attain that level of purity.) I believe that at this moment there are no lead mines in operation in the USA and no lead smelters, either. They all closed because the cost of compliance with EPA air emission regulation was too high for the operators of those facilities. (Now all the recycled lead is sent across the USA-Mexico border to be smelted in Mexico, where compliance with air emission standards is presumably easier.) Getting 99.99-percent pure lead is becoming more expensive. This is probably reflected in the higher cost of some AGM batteries that use very pure lead in their construction. But there is nothing intrinsic with AGM construction that means the lead in the AGM is higher purity.

In any production process, it may not be particularly cost-efficient to alter the production process to make inferior products to sell at lower prices. Just because DEKA sells their battery at the DEKA store for more than Costco sells the same battery to Costco members is not really a proof there is a difference in quality. Costco probably has a contract with DEKA to deliver a million batteries, so they get a better price from DEKA than you do when you walk in the DEKA retail store to buy one battery. Also, if DEKA undersold their OEM customers like Costco, that is, you could buy the same battery from DEKA at retail for less than you could from Costco, then customers like Costco would not be very happy with DEKA competing with them. Certainly Costco has a more efficient retail store delivery process than DEKA, so it is not surprising the cost of an item at Costco is going to be lower than elsewhere. That is more or less the entire reason to go to Costco--their price for any item is lower than at other retailers. Why wouldn't it be for batteries?

As far as I can tell, it is just complete speculation that DEKA would alter the lead purity in their batteries for different branding labels. If there is any evidence of this, let's have it.

[jimh]

ASIDE: the notion of "lower self-discharge" is really quite interesting to investigate. You find many vague mentions of this characteristic, but just about never find any data. In 2008 I investigated the difference in self-discharge rate between two random lead-acid batteries, one a flooded cell vented battery and the other an AGM battery. I found that the AGM had a lower self discharge rate, but the difference from a flooded cell lead-acid battery was only marginal. If interested in my findings on the self discharge rate of AGM batteries compared to flooded cell batteries, they are presented in a thread in the Old Forum. You will have to read past a great deal of introductory bluster by AGM-lovers to get to the data, so let me just present it here:

Self-discharge rate measured in lead-acid batteries

Non-AGM battery = 2.238 % per month

AGM battery = 1.731 % per month

That is a difference in self-discharge of about 0.5-percent per month. If you left the two batteries sitting for six months, the flooded cell would be about three-percent more discharged than the AGM. My data conforms exactly to one source I found that actually gave data about the comparable self-discharge rates of these two battery types. Yes, AGM is "better" and has "lower" self-discharge, but when you see the actual numbers, this difference becomes much less significant than the advertising department of many marine battery sellers would like you to think. If the cost of AGM batteries was determined by the difference in their self discharge rate, then maybe they would cost a few percent more than flooded cell batteries, but often they cost 100-percent more.

[Jefecinco]

Jim--It's interesting that the total discharge rate percentage is inconsequential. However, the AGM battery in your example self discharged almost 23% less per month than the flooded cell lead acid battery.

For an advertiser the 23% number is much more attractive. Next they will claim the AGM battery discharges 90% less during the four month Winter season compared to a flooded cell lead acid battery. Truth in advertising is something we've come to depend upon.

[jimh]

There are lies, dam lies, and then there are statistics.

Here is a good example: I put my truck away for the winter in early October. I started it yesterday. It fired up just fine after sitting for six months. I did not take any voltage measurements at the beginning and end of the idle period, but the battery had plenty of charge remaining to start the engine. The battery is a conventional lead-acid flooded cell battery. If I had spent three-time more for an AGM battery, I might have had a few percent more charge. Would it be worth the cost difference? Right after the engine started it began recharging the battery, and any difference in remaining charge that would have existed between my battery and an AGM was soon eliminated by the effect of the charging current.

If for some reason you have an application where you need a lead-acid battery to sit idle for two or three years and you need it to retain the most possible charge, then, okay, get the AGM if it is one of the few AGM batteries that use ultra-high-purity lead. You might have a good investment there. Maybe you need to leave something at the North Pole for two years before you will be back. Otherwise, I would not depend on the lower rate of self discharge as being a feature of the AGM to pay a lot for.

Now, that is not to say that there is no value in an AGM battery. I have never said that. I just want to make clear that the relentlessly repeated claim that an AGM battery has lower self discharge is not automatically true. It is only true if the AGM has ultra-high-purity lead. And, even it it does have lower self discharge, it is not all that much better than a flooded cell battery of similar quality.

[OldKenT]

Trolling motors take a large toll on batteries. My 24-Volt MinnKota 80-lbs thrust trolling motor will draw 56-Amperes at full speed— seldom used, of course. Depending on wind and current, one normally runs at maybe 20-percent to 30-percent of full speed, so the power demand is less, but over several hours of use, the drop in battery voltage and the resulting recharge requirements, are large.

Flooded cell batteries don’t do very well with the charge-discharge-charge cycle. AGMs are better, but how many charging cycles can one get before the ability of the battery to be fully charged and to discharge at the proper rate is significantly degraded?

Some manufacturers claim 300 to 350 cycles. Others claim 400 or more. Depending on the depth of discharge (DoD), some like NorthStar claim 900 cycles for their Group 31 AGM. But all of these are references to the number of charging cycles before the battery fails, and the failure process occurs over the life of the battery, so the batteries are continuously degraded. They don’t just suddenly fail.

Starting batteries are, I think, a different story because there is just a single draw which either is sufficient or not.

I was intrigued this weekend when I read about the Firefly Oasis Group-31 battery which uses carbon foam AGM and claims DoD of 80 to 100-percent without any loss of performance, up to 3,600 charging cycles at 50-percent DoD, and 1000 charging cycles at 80-percent DoD.


Most batteries would be DOA at that discharge percentage.

Practical Sailor has referred to these also, but has so far withheld endorsement, saying they need more experience.

Now, I don’t buy green bananas anymore, so perhaps it is better just to buy the $180 Duracell from Sam’s Club which jimh mentioned, and let my heirs worry about it. But, I am intrigued.

Has anyone here any experience with this Firefly battery? And does the technology sound right? There are articles on line that say that Caterpillar developed this technology and then spun it off to a new company which went into bankruptcy in 2010. The technology was bought out of bankruptcy by someone who has revived the brand.

Thanks to all who are advising on this. Very valuable help.
Ken

[Jefecinco]

There is a current article and discussion of batteries on http://www.panbo.com right now, and the Firefly brand is part of the article and discussion.

[jimh]

Part of the pitch for the $450 battery having actual lower cost over time is the claim it does not suffer from sulphation. Sulphation is a problem if a lead-acid battery is not allowed to float up to a terminal voltage of 14-Volts with a slow charge and be maintained at that level.

Most of the discussion on PANBO is with the perspective of long-range cruisers or sailors who are seldom at a dock with shore power. They are re-charging their batteries with available means, perhaps from periodic runs of their propulsion engine or from Photo-Voltaic sources.

My boat usage is just the opposite. The boat has access to shore power all the time. And a very high percentage of the time when not at the dock, the engine is running. So an AGM battery on my boat is essentially kept at full-charge all the time, and then only slightly discharged, then re-charged soon afterwards. I am not buying a $450 battery for that application.

If I were an angler and running an electric trolling motor until its batteries were just about flat, then perhaps a battery that provided more deep-discharge and partial-recharge cycles would be attractive. That sort of use sounds more like OLDTKENT's application.

However, if you are going to pay more that double for a battery, it better last more than twice as long. You haven't really saved any money, you just save the work of replacing the battery one fewer time.

[Jefecinco]

Jim,

Yes, agree with your remarks on the PANBO discussion.

If OldKenT is old as suggested by his forum "handle" he may value another value factor of AGM type batteries requiring virtually no maintenance over their lifetime. From my experience with them over the past 15 or so years they require no maintenance. The downside for old folks is their weight. Swapping out a couple of Group 31 batteries in a center console can be a very difficult chore. The effort of just getting them aboard a 190 Mountauk on its trailer was a challenge and required the use of a step ladder.

[OldKenT]

Butch and Jim,
As you both suggest, the best course is probably to continue using group 31 AGMs. Plus, a couple of articles including the one at Panbo suggest that Firefly may have some quality control problems. So, keeping it simple is probably best.
Here is a link to an article about Firefly's battery and its development by Caterpillar that you may find interesting:

http://www.sunshineworks.com/downloads/ ... nology.pdf

Searching for "carbon foam" also produced some interesting articles from government labs like Oak Ridge, and some research universities like Michigan Tech. It also seems that this material may be used to absorb radar. Many interesting applications.
Old is relative, I suppose, but these large AGMs seem to be putting on weight every year.
Ken

[jimh]

UPDATE: Here is a much easier to use PDF version of the document mentioned above. I much prefer this presentation:

http://www.sunshineworks.com/downloads/ ... nology.pdf

OLDKENT--thanks very much for the pointer and hyperlink to the article about the AGM carbon foam technology. I found the presentation method at the resource you initially linked to be hard to use. I found a better resource. See above.