AGM Batteries

Apr 11, 2017
571
Catalina C22 Solomon's Island, MD
Anyone have an opinion on AGM batteries?

I currently have 2 Optima AGM group 27 deep cycle batteries. After what is probably some poor charging practice on my part, they're getting near the end. I need to stay with AGM to avoid the potential dangers of off-gassing in an enclosed space. I don't mind buying Optima again, but thought I would see what else is available.

Duracell AGM group 27 deep cycle marine batteries are about half the cost. Has anyone had any experience with them?
 
Sep 25, 2008
7,075
Alden 50 Sarasota, Florida
All batteries are hopefully in an enclosed space. Or should be. If the myth that properly charged and maintained wet cells off-gas dangerously was true, most of us would be dead by now.
 
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Feb 26, 2004
22,759
Catalina 34 224 Maple Bay, BC, Canada
I need to stay with AGM to avoid the potential dangers of off-gassing in an enclosed space.
Urban myth. I've had wet cells on our C22, C25 and now our C34 (for the past twenty years).
The larger issue is what you mentioned:
After what is probably some poor charging practice on my part
...which is one of the downsides of AGMs.
These may be of interest to you:
AGM Batteries - Making The Choice (from Maine Sail)

https://forums.sailboatowners.com/index.php?threads/agm-batteries-making-the-choice.124973/

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
https://forums.sailboatowners.com/index.php?threads/darn-agm-batteries.133773/

Additional Observations on the Limits of AGMs http://c34.org/bbs/index.php/topic,5977.msg63004.html#msg63004

Your boat, your choice. :)

I wouldn't.
 
Apr 11, 2017
571
Catalina C22 Solomon's Island, MD
Thanks for the information. I had originally bought them for a 24v trolling motor on a different boat, and they basically sat unused for 2 years. Right now, they're mounted under the v-berth in a C22, and that's why I was concerned about any off-gassing issues.

I appreciate the links - a lot of good information.
 

jviss

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Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
Urban myth. I've had wet cells on our C22, C25 and now our C34 (for the past twenty years).
Well, I've never been hit by lightning, but I'm sure it happens to people. Under the right (wrong?) circumstances, hydrogen can collect and go boom. There have been hydrogen explosions on boats. If the PO thinks it's a risk, and he feels safer with a more sealed technology, that's good for him.

AGMs aren't all bad! You can routinely discharge them to 80% SOC without harm. So a pair of 100AH AGMs have more useable capacity than a pair of 100AH flooded batts - 60% more!

In addition, if your batteries are in a hard to reach place, you might not water them as often as you should. With AGMs that's not an issue.
 
May 24, 2004
7,129
CC 30 South Florida
AGMs are like Prima Donnas, they don't work for you, you work for them. I'll stay with my lead/acid wet cells as I can dish them some abuse and they are forgiving. Their best feature for me is that if one fails I can get off the boat anywhere and find a replacement.
 
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Sep 30, 2013
3,538
1988 Catalina 22 North Florida
BTW Hardhead ... you currently have two group 27's?? That is one helluva bank, for a 21.5' boat! Do you have a fridge on board, or something else I should be jealous of?? :biggrin:

Just thinking out loud here ... as long as you are replacing them, and you want a monster bank, have you considered group 31's? They are only 1/4" longer than group 27's (same exact width) but offer 25% more capacity. You could be rocking a 260Ah bank in the same footprint you have now. (Unless you have your AGM's mounted vertically, of course!) The only drawback is they weigh about seven pounds more.

Like I said, just a thought, and probably a thought you already had. Cheers!
 

greg_m

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May 23, 2017
692
Catalina Jaguar 22 Simons Town
Hydrogen is lighter than air... so it will find a hole somewhere and drift upwards and out the ventilation holes or hatchway. It does not collect in the bilge and go bang. Most of the time it's either way below or way above the explosive limits in any case.

AGM's were a development from aircraft batteries where you don't want liquid acid being thrown around from a broken battery whilst performing a less than ideal landing! That's pretty much the only real advantage to choose them IMO.
 
Nov 26, 2008
1,966
Endeavour 42 Cruisin
Virtually all boats older than 20 years had wet cells and if there was a real issue, it would have been addressed formally by USCG and ABYC to modify those hundreds of thousands of installations. My boat was designed with a large house bank under the master bunk 30 years ago. Still floating, no explosions. Do read the links provided above to mainesails dissertation on AGM batteries. The cost benefit/analysis favors, to me, wet cells by a long shot.
 
Apr 11, 2017
571
Catalina C22 Solomon's Island, MD
Thanks for the advice everyone. It seems crazy, but I use the battery capacity to run a laptop and 2 additional monitors when needed. (detachable to the aft bulkhead by the dinette) I like to take the boat out for 3-4 days when I can, and unfortunately need to keep up with hellish work obligations periodically to spare that kind of time away from the office.

That's a good point Gene -- it also just dawned on me I should probably be looking at group 31 when I replace them. I'd much rather go with tried and true wet cell batteries, but was basically concerned that with small cabin volume of a C22, I might be pushing my luck with any hydrogen gas discharge. It seems the real-life sentiment is that the issue of off-gassing is not too large of a concern in most cases.

Getting into the intricacies of battery capacities, solar panels and charge controllers is enough to bog one down with reading for a while. Thanks again for the great links-
 

SG

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Feb 11, 2017
1,670
J/Boat J/160 Annapolis
Optima's really aren't deep cycle batteries. I wouldn't today go with Lifelines from personal experience.
We have a supplemental "back-up" Precision Battery AGM 4D- AGM 240AH - 1000CCA that was recommended by Marine Electric in Annapolis. (Patrick Tewes)

Outgassing is an issue in closed spaces. AGM's are MUCH better than Gel which is much better than lead acid batteries. Better = LESS outgassing. AGM's have almost none and are much safer in that regard.
 

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
AGM's were a development from aircraft batteries where you don't want liquid acid being thrown around from a broken battery whilst performing a less than ideal landing! That's pretty much the only real advantage to choose them IMO.
- An AGM battery has a much higher bulk charge acceptance rate than a FLA, if you have the charger or alternator to take advantage of that charge rate you can top off your batteries quickly, an advantage for cruisers or anyone who doesn’t like listening to an engine run.
- An AGM does not percolate and spit acid so you don’t have to contain them and you can put them in places where a FLA would destroy stuff.
- An AGM doesn’t require regular access and watering, so you can tuck them away and leave them.
- An AGM will hold its charge much longer than a FLA - no need to drag them home for the winter.
- An AGM is a sealed battery, if you swamp a FLA in seawater it will produce chlorine gas.
- An AGM doesn’t release hydrogen gas, an FLA does and it is in a container where the gas can collect, if it is not in a container, see comment #2.
 
Oct 1, 2007
1,856
Boston Whaler Super Sport Pt. Judith
I don't know anything about the technical characteristics of AGMs but I do have a real life story. A friend of mine with a sailboat about the same size as mine invested a huge amount of money in 3 AGM house and 1 AGM start the same season we first launched Maxine, who has 3 gel house and 1 gel start. My friend is now on his 3rd set of AGMs (huge investments-I could never understand why he keeps going back) while my gels are still perfectly fine after 11 seasons.
 
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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
...Duracell AGM group 27 deep cycle marine batteries are about half the cost. Has anyone had any experience with them?
I am on my second set of 3, 31 Duracell batteries in my B323. good price of 94.95 at Sams CLub. 1st set went 6 years.
 
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greg_m

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May 23, 2017
692
Catalina Jaguar 22 Simons Town
- An AGM battery has a much higher bulk charge acceptance rate than a FLA, if you have the charger or alternator to take advantage of that charge rate you can top off your batteries quickly, an advantage for cruisers or anyone who doesn’t like listening to an engine run.
- An AGM does not percolate and spit acid so you don’t have to contain them and you can put them in places where a FLA would destroy stuff.
- An AGM doesn’t require regular access and watering, so you can tuck them away and leave them.
- An AGM will hold its charge much longer than a FLA - no need to drag them home for the winter.
- An AGM is a sealed battery, if you swamp a FLA in seawater it will produce chlorine gas.
- An AGM doesn’t release hydrogen gas, an FLA does and it is in a container where the gas can collect, if it is not in a container, see comment #2.
Well thank you for this very informative piece on the advantages however to balance it lets look at the disadvantages too:

- Higher manufacturing cost than flooded (in some cases extremely significant especially when you get to the more exotic chemical types)

- Sensitive to overcharging (AGM has tighter tolerances so your ordinary alternator voltage regulator just won't do it = a more expensive charging control system needs to be installed)

- Capacity has gradual decline (has a performance dome so as with everything else they don't last forever), see point one of disadvantages above

- Low specific energy (meaning they do not actually have the heavy duty grunt that a good solid FLA battery can provide)

- Must be stored in charged condition (less critical than flooded)

What we are talking about is a 22 foot boat and battery applications, your own preference, your own prejudices, your own wallet size! Each will have their own...
 
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Apr 20, 2016
47
Catalina 22 293 Huntington Lake, CA
I have used Optima yellow and red top for different automotive applications, but last year switched to the Exide Edge AGM version from Advanced Battery Systems (ABS)for my F-250. You can find them on the www and the people who answer the phone know people who can answer your questions. And their prices are very competitive, regardless of what product you choose. Including shipping.... BUT, as you indicated, your charging practices may have caused an premature passing of your AGMs. You need to use a specific charger, like the Optimate, that varies the voltage and amperage in the charge, "Keeping it fresh" you know... And, anything with liquid in it can leak if given the opportunity.
 
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