AGM Batteries

Looking for real life experiences of using AGM batteries for your house bank, especially those who spend a lot of time on the hook. Compared to the lead acid golf carts that I'm currently using, AGM's have no maintenance, charge quicker and can be safely discharged further. The only rub that I see is cost, about double that of LA batteries. How about useful life? I change my 8 golf carts every five years. How long do AGMs last?

I found them to be about the same as flooded. Just no maintenance which is nice, and the other advantages you mention.

twistedtree said:

I found them to be about the same as flooded. Just no maintenance which is nice, and the other advantages you mention.

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TT, I was just down at docks and noticed your ex boat, Puffin Quest. Looks to be the biggest in the NWX charter fleet, the next down being a Fleming and a big KK. The design of your boat to me is the best of what NH has built....really a nice line to it.

Ken E. said:

TT, I was just down at docks and noticed your ex boat, Puffin Quest. Looks to be the biggest in the NWX charter fleet, the next down being a Fleming and a big KK. The design of your boat to me is the best of what NH has built....really a nice line to it.

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Thanks. Yes, it was a great boat and served us well.

Ken E. said:

Looking for real life experiences of using AGM batteries for your house bank, especially those who spend a lot of time on the hook. Compared to the lead acid golf carts that I'm currently using, AGM's have no maintenance, charge quicker and can be safely discharged further. The only rub that I see is cost, about double that of LA batteries. How about useful life? I change my 8 golf carts every five years. How long do AGMs last?

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We've used AGMs since early 2006. Twp large dual-purpose banks (half the house each, plus an engine start).

The oldest of those banks was 300 Ah of 3x Odyssey PC-2150s (G31s) installed in early 2006, lasted about 12 seasons.

We replaced that with 4x Lifeline GPL-4CTs in late 2017 (440 Ah), after I figured out how to better use that available space to increase capacity. Then we also installed a 70A inverter/charger dedicated to that bank. Too early to tell about longevity.

The second of those main banks is the same size, installed in mid-2009, still going strong. Original 40A charger.

We also have an AGM genset start battery, an Odyssey PC-1500 (G34), also installed in 2009, no signs of age yet.

We don't anchor much longer than a couple weeks at a time, though.

-Chris

Does anyone routinely charge their AGMs at more than .25C or draw them down routinely below 50%?


David

our old Defever had all lifeline AGM 8GCs 3 8ds and a pair of L16s They were 8 years old and still going strong..... The boat we just purchased has fullriver AGMs they are reported to be 5 years old and all have to be replaced. Both boats have the same inverter/ charger so I would guess they similar charge characteristics. ALot of the decision between FLA and AGM depends on ease of battery access and will the boat be untended to for a long period of time.... in our case the answer is AGMs

My AGM house bank experience is mostly with 12V g31's, mostly East Penn Deka (also sold at Sam's Club under the Duracell label - current price $155 until December 24).

House bank (2 x Deka g31) on my 26-foot cruiser lasted 11 summers, anchoring 65-75% of the nights. After that it had Sears Die-Hard (Odyssey) g31 AGM's for 4-5 years before I sold it.

Installed 4 Deka/Duracell AGM's for house bank on Dream Catcher two years ago, with 2 for start bank, and 2 for bow thruster/windlass. There's an Optima g31 of unknown age (at least 3 yrs) for the stern thruster. All fine so far, but no meaningful longevity data yet. BTW, the start and bow banks I replaced were each single Deka 4D Gel's, original equipment in my 2002 NT37, just beginning to die after the 2016 summer season.

Had a pair of Optima spiral-wound AGM's which lasted 10 years starting my diesel pickup tow vehicle, including sitting out in Northern Utah snow every winter. When they were 9 years old, I left the truck parked for a 3.5-month summer cruise of BC. When I returned, they easily started the truck's big Cummins. The truck has sat waiting for me to return from a 2-4.5 month summer cruise for ~18 years, and was never hard to start. Right now it has a pair of Deka g34 AGM's, about 6 years old.

A pair of Optima's for starting the 26-footer's Volvo diesel lasted 6-7 years.

Both boats had good externally regulated alternators, and battery monitors. Both would charge at .3C or a bit more if the house bank was discharged down near 50%.

One might suspect I like AGM's.

"One might suspect I like AGMs"

Roger that, Richard!

When we bought our boat we had 2 <1 year old 8D AGMs in place. PO bought them at West Marine for about $700 each. They performed well until after our 3rd summer storage. During the 2nd season the main engine alternator voltage regulator went high output voltage coming out of the slip when I brought the throttle up. Voltage was 16.5 on the FB which means about 17.0 down at the batteries. We cut the trip short and returned to the dock with voltage bouncing anywhere from 11.5 to 17.0 for about 20 minutes of runtime. For the rest of the season the capacity seemed to be dropping rapidly. Each season when I get back to FL, one of the first things I do is take an "as-found" voltage reading of the batteries. Previous years they would be 12.55 V or so after 6 months of storage. That year, 8.5 and 9.1 volts. They would not take and hold a charge. That was it. Poof, $1400 gone. In goes 6 - 6V Trojan T105s. So far so good.
So for me personally I would not recommend AGMs unless access is bad for the required water addition of Flooded Lead Acid batteries or they need to be stored somewhere without decent venting or the price comes down by half. If they were within 10% price of T105s, yes sure.

One advantage of AGM over FLA is that you can mount AGM on their side.
I was able to move mine from next to the engine to outboard of a side stringer by putting them on their side. Doing that gave me much better access to the starter on the engine.

First of all, there are high quality and low quality AGMs. Lifeline brand are on the high quality end, the ones in the sailboat were purchased in 2006 and still seem fine. I've had them in other uses (RVs, aerial work platforms, other boats) and if cared for, they've always gone at least 10 years.

One caveat on AGMs - they require a full charge periodically (like once a week or so) or they will sulfate and lose capacity. If you spend long periods in one place on the hook, and don't have solar or some other passive means to charge, that requires running the genset for 6-8 hours.

I routinely charge the ones on the sailboat at 0.5C, if they are down. It is a 440 AH bank and if at 50% SOC will accept about 250A for a little while. The AH counter ticks off at about 1 every 15 seconds, fun to watch for a short while. The advantage of charging fast depends on your charging system's ability to supply the current, and they still have a very long tail to get to 100%, so the effective time to recharge isn't that different than flooded. To recover from 50% to 80% will be different, if you have the charger to do it.

There is a technology called carbon foam, these are AGMs with a unique plate material. They do not suffer sulfation from operating for long periods in a partial state of charge. However if you don't like the cost of AGMs, you really won't like the cost of the carbon foam version.

My experience with a large AGM bank is the same as Twisted's. Not much difference over LA, as near as I could tell, other than lower maintenance. Like LA, they take a long time to FULLY charge, which as others have noted, is critical for longevity. Mine were still good after 10 years, replaced with Lithium.

Been using agms for a pretty long time for underwater lights and dpv’s in fl caves mainly because as hopcar mentioned they can be turned on their side. Whether they make sense or not totally depends on how you use and run your boat. We bought our current boat in 2012 with 6 month old agm batteries. We replaced them in May 2017. On average we have spent 250 nights per year on the hook. We never discharged them more than 40 percent and quickly recharged them back to 95%. Our house bank is 24 volts and composed of 4 banks of 2 lifeline 8ds. We can charge a single bank at .8C or the whole bank at .2C. We have an auto start on our small genny and we program it to maintain the bank between 80 and 95 percent depth of discharge among other things. Once a week we bring the whole bank to full charge. We can do this one of two ways, either bank by bank hammering each bank at a higher absorb current by one of the chargers for a few hours,or by trickle charging all four banks overnight while running the inverter charger with different settings and the ac. We purposely chose to add a small genny (more versitile) rather then mess with wind or solar to accomplish this. I believe this time we should get more than five years out of our batteries because we are now with the new genny and charging routine abusing them less but we won’t know for real until 2022. Lifeline says 1500 cycles in a perfect world, so cutting that in half due to stuff happening and being on a boat and so forth they still should beat 5years. Five years from now I really don’t think I’ll care, I’ll be changing them regardless. My brother still runs lead acid golf cart batts in his boat which is up north in your neck of the woods. He’s on the hook maybe 60 nights of the year with his setup and he replaces them every five years. His bank costs him considerably less than ours yet we are both happy... go figure. Btw as far as agms charging quicker, they do up until about 95% whereas your lead acids begin to taper off at about 70%. Usable amps however are similar in that below 50 dod you reduce life and capacity greatly although five years should not ever be an issue for either chemistry. My gut instinct says to stick with the Gc’s for your needs and invest the rest somewhere else as long as you can easily get to the cells to check and maintain the specific gravity readings. If you can’t your running blind and are probably better off making the switch.-

[FONT=&quot]Over the past 20 years, WESTERLY has had the following house banks. What hasn’t changed is how the boat is used: Frequent anchoring with a full 100% restorative charge not happening for 7-10 days or so. The generator has always been used to make hot water in the am and pm, and bring the house bank up to 80% at dinnertime. Normal usage is between 65-80%, unless cruising or on shore power.[/FONT]

[FONT=&quot]The First House Bank: Sep 1998 to July 2004[/FONT]

[FONT=&quot](10) 6VDC golf cart batteries (Dyno Model 2GCb 245Ah ea) are wired in series and parallel to provide 5 sets of 12VDC (Total Dyno rated 1225Ah) in a single accessory bank. Provided around 200,000 amps.[/FONT]

[FONT=&quot]The Second House Bank: July 2004 to April 2013[/FONT]

[FONT=&quot](10) 6VDC golf cart batteries (Gel-Tech Model 8GGC2 180AH ea) are wired in series and parallel to provide 5 sets of 12VDC (Total rated capacity 900AH) in a single accessory bank. Provided around 280,000 amps.[/FONT]

[FONT=&quot]The Third House Bank: April 2013 to April 2016[/FONT]

[FONT=&quot](8) 6VDC golf cart batteries (Lifeline Model GPL-4CT AGM, 220Ah ea) are wired in series and parallel to provide (4) sets of 12VDC batteries (Total rated capacity 880Ah) in a single accessory bank. [/FONT]

[FONT=&quot]After isolating the batteries and checking for bad cells, the batteries were removed from service after 3 years and 50,000 amps service, a poor showing but apparently not uncommon for a deep cycle AGM battery bank that had to deal with partial state-of-charge issues as part of the boat's cruising/charging profile (According to Lifeline). [/FONT][FONT=&quot]This factory information was not available when these batteries were researched and purchased/installed. A series of articles on the Attainable Adventure Cruising website documented the need to frequently condition these batteries based on Lifeline factory input. For a Partial State Of Charge (PSOC) charging profile, these batteries require a lot of maintenance, and are best for boaters who cruise between marinas where they are seldom used and always charged, or who may have a large solar panel charging system (and frequent sun).[/FONT]

[FONT=&quot]The Fourth House Bank: April 2016 to present[/FONT]

[FONT=&quot](6) 12VDC group 31 batteries (Firefly Oasis 12V G31, 116Ah ea) are wired in parallel to provide 696Ah of total capacity. [/FONT]

[FONT=&quot]These carbon foam batteries are designed to resist sulfating from PSOC operations. Good experience so far.[/FONT]

Great comments and very helpful.

Note to Jay .....when we were in Sitka in July, someone said you were in the neighborhood. Were you up there last summer? Going up next year?

Ken. Will send you a pm. Jay

We may have the record on our Lindell 36, 4 lifeline GPL-8DA’s, from 2002, still going strong.
Eric

in 2008 I remade my house bank with Fullriver agm 6v units as shown.

My boat does not have a generator.

I use around 120 amps per 24hrs.

Charging is handled by a large frame 200amp alternator with smart regulation, or at the dock by a 75A IOTA charger.

We typically are out 45-60 days during the summer in the PNW.

Anchoring 95% of the time.

The bank is sized to allow up to 5 days at anchor without starting the main.

We typically only stay anchored in one spot for a max of 4 nights.

I don't keep track of the number or exact depth of discharge prior to a recharge, but it is rare that it is less than 75%.

The bank is now 10 seasons old and as far as I can tell it performs the same as the day it was installed.


In 2008, Fullriver was just arriving in the mainstream, so it was a bit of a gamble, but I had found some fairly re-assuring comments from battery guru's in the know.

YMMV

djmarchand said:

Does anyone routinely charge their AGMs at more than .25C or draw them down routinely below 50%?


David

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Yes, on the charge rate, but not a lot more. Just under .3C. I don't think it really gets you charged any faster. The bank just reaches absorb sooner, then takes longer in absorb. I don't know what the break point is, but at some point there is a diminishing return on higher charge rates.


No on drawing below 50%

Jay:


Your battery experience is illuminating. It was interesting that you provided total amps in and out in addition to years of service. Do you believe that total amps is more important in gauging service life?


I will be very interested in what you have to say about the Fireflys in another three years or 200,000 amps, whichever comes first. They sure are expensive though!!


David

My first set of house LAs went 8 years, still doing fine at that point but why not change them out, they were cheap. The second set went for 7 years and were doing fine, but changed them out too. They were cheap. My 11 LAs are easy to service, so maintenance not an issue.

My first set of bow thruster AGMs went five years, they were shot, they were not cheap. But being as in the cabin space, AGMs a good choice.

But boating is not really about saving money, for most of us anyway. So Firefly or Li are still on the radar. But the decision is not easy, because for some strange reason our LAs charge quickly enough to easily keep up with our cruising style.

It is not too surprising that lead acid golf cart batteries work well in marine house battery service. That service is somewhat similar to the useage profile for golf carts. In that case a couple of golf cart batteries put out maybe 50 amps pushing the golf cart periodically for a day. Then they are fully recharged. Boaters use less peak amps typically (except for very brief microwave or coffee maker use from an inverter) and don't recharge fully every day. But maybe close enough.

Electric golf carts have been in use for what maybe a century. The industry developed a battery that worked well in that service over those many years. Any manufacturer who cut corners was immediately found out and driven out of that market.

That is why there are very few if any bad FLA golf cart batteries. Trojan T105s are good by not 50% better than Interstates.

I am a little surprised at the posts above describing less useful life from AG batteries but only a little. Maybe AGMs aren't as optimized for golf cart use as FLA GCs are.

I also wonder about AGMs supposed ability to accept a greater charge rate than FLAs. I know the above posters have said that they charge at .3-.5C but how do we know you can't do the same with FLAs?

So from the above analysis I don't know what to believe about AGMs longevity and charge acceptance rate vs FLAs.

Does anyone have any real data on self discharge rates for AGMs vs FLAs. I know that a good FLA will still start a car after sitting for 6 months.

David

David, just a personal, noon empirical observation, but I felt my AGM bank started out at a higher rate of charge, but pretty quickly that subsided and they wouldn't accept all that I could throw at them. Ending up looking like LA over the entire charge cycle, with the same very long taper to get fully recharged.

David
There is a human element involved here, self supporting one's choices. I've been guilty many times. Simply stated, if one were to spend 2-3X the cost for a full set of AGMs they would be better, last longer and in all ways superior to LAs - and often not admit otherwise.

As many have done and so stated here by TT and others, lack of easy access to top up LAs is a perfectly acceptable enough reason to change. D Hayes had a good write-up over a year ago on why he went with AGMs on his North Pacific.

Here is the quick start manual from lifeline which contains some useful info. You can also download the full manual on their website. Self discharge rate is 2%/ month.




FWIW I just changed out a set of 4d agms that lasted over 11 years before they would no longer start our port engine. These batteries were always isolated and not maintained by a charger unless paralleled with the house batts when charging. They were solely maintained by an on engine dedicated “not so smart” alternator which provided around 600 hours of charging per year for the last decade or so. The max charging output for this alternator is .28C.

As far as energy storage and use goes, our house bank when new was rated to be 1020 amps @ 24v = 24.4 kw. Our daily energy needs seem to average around 4800 watts per day(200 amp hours@24v). That plus about 2% more is required to bring the bank back up to full charge. So extrapolating 250days/year*200amp hrs/day*5=250,000 amps and appears to yield similar numbers.

Trojan lists the self discharge rate of the T105s at 5-15%/month based on storage temperature conditions. We have Optimas for our generator’s and starting bank with no charger on either. I’ve gone 4 months and they both start fine.

https://www.trojanbattery.com/pdf/datasheets/T105_Trojan_Data_Sheets.pdf

David asks:
Does anyone have any real data on self discharge rates for AGMs vs FLAs. I know that a good FLA will still start a car after sitting for 6 months.

I fully isolate my completely charged agm house bank and leave it so from Oct. through June. I will check the standing voltage around once per month. I may run the shore charger about once every 2 or 3 months for a couple of hours, but the batteries really do not self discharge much, voltage may drop from 12.8v to 12.7 in the couple of months.



To the question of justifying the purchase of AGM with optimistic results, I was pleased to find these batteries back in 2008 for about $20/ea. more than FLA golf carts, so the cost was pretty much what wet cells would have been.

I believe the longevity I am experiencing has more to do with the enormous size of the bank vs. the draw down. I don't think this bank has ever been at 65% or lower during its life.


AGM's were a great option for me as I wanted to stack the bank along the curve of the bilge, somewhat askew of level, which would not have worked for wets.

Without knowing the quality and the care given in many of these anecdotes, the data is noisy. Flooded batteries tolerate abuse better than AGMs, and many owners unknowingly abuse their batteries. The Fireflys will tolerate this abuse as well.

If you don't know much about your charging system and it isn't set up for AGM batteries, you will be better served with flooded batteries. They are less expensive to replace and will last longer poorly treated.

In any discussion of cost - provided you are going to own the boat for the entire battery life - then life cycle cost is a better measurement than initial cost. How many Amp Hours are delivered over their life divided by the initial cost. In life cycle cost, the Fireflys will beat the other LA chemistries, and LFP will beat them all by a wide margin. Capital cost is higher but greater AH delivered over their life more than makes up for that. Across that one must consider use case: living on the hook and charging when you can? LFP. Weekend use and plugging into the marina otherwise? FLA or AGM. Good charging source but used intermittently? AGM.

cafesport said:

As far as energy storage and use goes, our house bank when new was rated to be 1020 amps @ 24v = 24.4 kw. Our daily energy needs seem to average around 4800 watts per day(200 amps @24v). That plus about 2% more is required to bring the bank back up to full charge. So extrapolating 250days/year*200amps/day*5=250,000 amps and appears to yield similar numbers.

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Thanks for sharing.

The Lifeline house AGMs in the N55s are a very nice arrangement. Likely not anyone would consider FLA for your application. Do you have two inverter chargers, if so what size and charging capacity?