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AGM Batteries - Making The Choice

Aug 22, 2017
1,592
Hunter 26.5 West Palm Beach
...
Low self discharge - This is great for boats in hot climates or on moorings. Wets can self discharge at up to 13+% per month in warm weather however I know few boaters who go a month without using the boat at all. Even in a worst case scenario, 13%, in hot weather leaves a full bank still at 87% SOC after a month. Still this can be a good benefit in certain use situations. Self discharge has never been an issue for me so would not be weighed in my own benefit analysis. If you're buying AGM batteries specifically for the low self discharge a small solar panel will eliminate the self discharge issue and cost considerably less than the price difference between a bank of AGM and flooded.
...
Wow, TONS of good info in that write up. Thank you for posting.

The above paragraph does leave me with a question. It's been my experience that after a battery has sat at PSOC for more than a day or two, the self discharge rate tends to go up noticeably. I have always assumed that this comes from sulfate bridging, but I have no real proof of that. If the battery (especially a cheap one) is left to sit for a longer period of time, the effect seems to accelerate.

Have you noticed similar increases in self discharge rate?
 

Rick

.
Oct 5, 2004
1,052
Hunter 420 Passage San Diego
And then there is Lithium. Maine Sail does not consult on lithium, but he can "water your eyes" with um "stuff" about them. Also a plug. He has a lot of stuff that all of us need for sale electrically on his site.
Great article! I dont have AGMs but I read every word.
 

Bob S

.
Sep 27, 2007
1,552
Beneteau 393 New Bedford, MA
I just purchased a Northstar Group 27 AGM for a start/reserve battery and six GC2's for the house.
  1. Do you do anything to commission the AGM? This battery will most likely never be needed and will be fed by an echo charger (I am following your advise for the 6V in parallel from another thread)
  2. Is it recommended to use a battery box for a single AGM? I was thinking of fabricating an aluminum base that can be fastened down and use two stainless steel threaded rods and a bracket to hold it down similar to that used in cars.
 
Aug 22, 2017
1,592
Hunter 26.5 West Palm Beach
And then there is Lithium. Maine Sail does not consult on lithium, but he can "water your eyes" with um "stuff" about them. ...
Yea, Lithium, can be a great performer with a great power to weight ratio, but you need to have the right guy keeping an eye on the system & you need the right kind of cell-level monitoring as well as the right kind of charger. When bad things happen with Lithium systems, the results can be catastrophic.
 
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Gunni

.
Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
  1. Is it recommended to use a battery box for a single AGM? I was thinking of fabricating an aluminum base that can be fastened down and use two stainless steel threaded rods and a bracket to hold it down similar to that used in cars.
An
An AGM does not require a battery box, BUT I have my starter battery in a box because it is in my engine bay where falling wrenches, tools and miscellaneous engine parts could possibly contact the battery cables and cause a catastrophic short. It was also easy to grab one off the shelf and strap it in.
 

Johnb

.
Jan 22, 2008
1,194
Hunter 37-cutter Richmond CA
I believe every battery should have containment. Prevents shorts, is a line of defense against cracking and also helps keep the battery clean.
 
Feb 6, 1998
11,258
Canadian Sailcraft 36T Casco Bay, ME
I believe every battery should have containment. Prevents shorts, is a line of defense against cracking and also helps keep the battery clean.
"Containment", in the ABYC context, is for catchment of any leaked electrolyte. Batteries classified as non-spillable eg: AGM batteries do not need a form of acid containment because even when broken open they don't leak electrolyte.. They do need terminal protection from shorting though. This can be in the form of terminal boots or a dedicated battery compartment with lid. Of course most instances of shorting battery terminals happens when the lid is off and your working on the batteries. This is why stubby insulated battery wrenches should be standard equipment for a boat owner. Plasti-Dip is your friend.

If you have batteries that can leak electrolyte, the box into which they could leak acid needs to be acid tolerant. It also needs to be able to contain the acid in the battery without spilling to areas that are not acid tolerant, with consideration given to vessel type & usage. Containment, for batteries that have liquid electrolyte, should be capable of containment at angles of typical heeling on a sailboat.

Many boat builders molded fiberglass battery boxes, Ericson, Pearson etc., and those meet the requirement, as does a $6.00 plastic battery box. However if you put a SS screw through the bottom of the battery box or floor of a fiberglass battery compartment, as far too many people do, it can no longer withstand "electrolyte attack" unless the fastener is isolated so that acid erosion of the fastener would not allow the electrolyte to leak out....

If one needs a custom box, often better than a cheap Tupperware grade battery box, they are easy to custom build out of plywood.. You then drop it at a Rhino Liner and have them hit it with pickup truck bed liner.

Dry batteries, eg: AGM's, that can't leak electrolyte would not require accommodations for acid spillage or leakage, because they can't physically leak, but flooded batteries would.

When battery acid gets to keel bolts, it's not pretty, and it gets very expensive. I have seen far too many flooded batteries leak or crack and when there is no containment it gets nasty. Even with containment it can be a nasty mess of corrosion...

Perhaps the easiest method to determine whether acid containment is necessary is to simply read the MSDS for your battery or contact the manufacturer. I know of no deep cycle flooded batteries that meet the DOT or CFR 49 classification requirements for "non-spillable". Most all AGM and GEL batteries however meet the "non-spillable" requirements under DOT and CFR 49 as "non-spillable".
 
Apr 8, 2011
250
Hunter 36 Deale, MD
So I’m looking at replacing my house batteries on my 2009 H36 within a year and doing some research. I’ve read this thread and done some reading in Marinehowto as well. I’ve installed a Victron BMV-712 monitor, and am nearly done installing 160 watts of solar run thru a Victron 100/20 MPPT. Currently have PO installed 2 4D Deka (WM branded) 198 Ah AGMs and a ProMariner ProTech i 1230i Plus shore charger, and a stock 60 amp internally regulated alternator and belts on the 3YM30. The reason I’m considering replacing is the batteries are original (I’m fairly certain), and capacity loss is substantial, though I’m still working on a test as you have prescribed to get a tighter figure on capacity remaining. My usage is mostly Day/weekend overnight sails, with occasional 7-10 day trips away from the slip. Otherwise the boat is plugged in and the charger engaged. My energy consumption is 130Ah/24 hrs away from the dock. I sail on the Chesapeake bay.

I’m leaning toward 3 paralleled Group 31 110Ah Firefly batteries. I’m primarily interested in thoughts on what I may need to do with regard to my alternator and/or shore charger, if anything. I would like to maximize the life on the Firefly batteries. Other suggestions welcome.
 
Nov 2, 2017
9
Delphia 37 Bayfield
So I’m looking at replacing my house batteries on my 2009 H36 within a year and doing some research. I’ve read this thread and done some reading in Marinehowto as well. I’ve installed a Victron BMV-712 monitor, and am nearly done installing 160 watts of solar run thru a Victron 100/20 MPPT. Currently have PO installed 2 4D Deka (WM branded) 198 Ah AGMs and a ProMariner ProTech i 1230i Plus shore charger, and a stock 60 amp internally regulated alternator and belts on the 3YM30. The reason I’m considering replacing is the batteries are original (I’m fairly certain), and capacity loss is substantial, though I’m still working on a test as you have prescribed to get a tighter figure on capacity remaining. My usage is mostly Day/weekend overnight sails, with occasional 7-10 day trips away from the slip. Otherwise the boat is plugged in and the charger engaged. My energy consumption is 130Ah/24 hrs away from the dock. I sail on the Chesapeake bay.

I’m leaning toward 3 paralleled Group 31 110Ah Firefly batteries. I’m primarily interested in thoughts on what I may need to do with regard to my alternator and/or shore charger, if anything. I would like to maximize the life on the Firefly batteries. Other suggestions welcome.
We have many similarities from boat size, usage patterns, boat age, engine etc. Having gone through the process of upgrading basically everything on my boat I can give you my thoughts/justification. In general, my decisions were value based.

Batteries - I was very torn on this, waited in the Firefly order queue for 6+ months and finally my turn was up... I ended up passing on Firefly’s and went with 3x East Penn (Napa) g31 gel batteries. Just installed them last weekend, too soon to know if this as the right decision. For me this ended up being a value play, boat is a seasonal use (Lake Superior) and sits in the hard for half the year. 3x Firefly’s were close to $1700, the East Pen gel were $740 or so for the 3x. I know I technically could have gone with 2x Firefly’s but the weight saving is not a huge deal to me as I’m mostly a cruiser. Rod and Bruce Schwab Have nothing but positive things to say about gel’s so long as you charge them right, fingers crossed!

Alternator - I went with Rod’s CMI-80 and a Balmar MC-614. Again, price to performance play. I have it belt managed to level 3 (15%) and on the old batteries (3x East Penn AGM (West Marine)) saw ~62 or so amps out of the alternator last year. Again I hemmed and hawed over a Balmar alternator or Mark Grasser but for the extra maybe 20 amps only during the short period the batteries can accept the high current it just didn’t make sense. Old alt was stock 60amp Hatitchi which put out maybe 20 amps at most. Got all the temp sensors and wired direct voltage sensing wire per Rod’s install guide. I really want a serpentine belt conversion kit but that’s silly for my size and use setup, I went from no belt dust to some so I need to figure that out.

Solar- I did 2x 100w flexible panels (Chinese ones) on the Bimini with a Morningstar SunSaver controller. I picked that controller as it was the the only one with every option possible in this size range- temp sensor, fully controllable and I forget the other reasons. I likely slightly overbought on the controller but my boats name is also Morningstar so...:). Rod would cringe at the actual output vs. rated on these panels, but at 20% the cost of Solbian it works for me. My usage is actually only in the 60-80 amp hours/day so only getting 6-8 amps out of the panels is ok. Plus the long days up here help up the amp hour count.

Shorepower charger - Promariner 40amp. Seemed like a no brainer, temp sensors installed with custom charge settings.

Anyways, that’s what I did. Too soon to know how well it all works. I really wanted Firefly’s but for a weekender/seasonal use boat with a few week long trips I just could not justify it. Part of me thinks in a few years I could just jump to Li depending on how long I keep this boat.

Ps put LED bulbs everywhere! Huge reduction in my electrical budget.
 
Oct 22, 2014
12,573
CAL 35 Cruiser Portland OR, moored EVERETT WA
Practical :dancing: @marty9876.
Spending money wisely on solid proven equipment is a good thing. It makes for more sailing with a high degree of safety, and more money in the cruising kitty.
:worship:
 
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Apr 8, 2011
250
Hunter 36 Deale, MD
We have many similarities from boat size, usage patterns, boat age, engine etc. Having gone through the process of upgrading basically everything on my boat I can give you my thoughts/justification. In general, my decisions were value based.

Batteries - I was very torn on this, waited in the Firefly order queue for 6+ months and finally my turn was up... I ended up passing on Firefly’s and went with 3x East Penn (Napa) g31 gel batteries. Just installed them last weekend, too soon to know if this as the right decision. For me this ended up being a value play, boat is a seasonal use (Lake Superior) and sits in the hard for half the year. 3x Firefly’s were close to $1700, the East Pen gel were $740 or so for the 3x. I know I technically could have gone with 2x Firefly’s but the weight saving is not a huge deal to me as I’m mostly a cruiser. Rod and Bruce Schwab Have nothing but positive things to say about gel’s so long as you charge them right, fingers crossed!

Alternator - I went with Rod’s CMI-80 and a Balmar MC-614. Again, price to performance play. I have it belt managed to level 3 (15%) and on the old batteries (3x East Penn AGM (West Marine)) saw ~62 or so amps out of the alternator last year. Again I hemmed and hawed over a Balmar alternator or Mark Grasser but for the extra maybe 20 amps only during the short period the batteries can accept the high current it just didn’t make sense. Old alt was stock 60amp Hatitchi which put out maybe 20 amps at most. Got all the temp sensors and wired direct voltage sensing wire per Rod’s install guide. I really want a serpentine belt conversion kit but that’s silly for my size and use setup, I went from no belt dust to some so I need to figure that out.

Solar- I did 2x 100w flexible panels (Chinese ones) on the Bimini with a Morningstar SunSaver controller. I picked that controller as it was the the only one with every option possible in this size range- temp sensor, fully controllable and I forget the other reasons. I likely slightly overbought on the controller but my boats name is also Morningstar so...:). Rod would cringe at the actual output vs. rated on these panels, but at 20% the cost of Solbian it works for me. My usage is actually only in the 60-80 amp hours/day so only getting 6-8 amps out of the panels is ok. Plus the long days up here help up the amp hour count.

Shorepower charger - Promariner 40amp. Seemed like a no brainer, temp sensors installed with custom charge settings.

Anyways, that’s what I did. Too soon to know how well it all works. I really wanted Firefly’s but for a weekender/seasonal use boat with a few week long trips I just could not justify it. Part of me thinks in a few years I could just jump to Li depending on how long I keep this boat.

Ps put LED bulbs everywhere! Huge reduction in my electrical budget.
Marty:

Thanks for taking the time to share your experience. I hadn't seen any responses here, so I started a new thread and posed the same question. There are some very helpful responses in there, including one from Maine Sail. Here's the thread, in case you're interested:

https://forums.sailboatowners.com/index.php?threads/firefly-batteries-and-the-rest-of-the-charging-system.196179/

The consensus - which was really valuable - is that my usage as outlined in my post doesn't warrant Fireflies, or even AGMs, according to Maine Sail. And to properly install the batteries and the right charging system would be pretty expensive, requiring an upgrade to my shore charger and an externally regulated alternator and pulley upgrade. That sounds right - if I understand Maine Sail's extensive writing on the subject of AGMs and their proper care and use.

I think I'm headed down the path of FLAs, and possibly an alternator and pulley upgrade, based on the consensus of my use case. I have everything done for my solar install, but am just waiting for the panel to be sewn to the bimini. I'm anxious to see what I get in terms of Ah from the 160w Renogy panel before I start on the charging system.

Are you planning on taking the solar power equipment credit on your taxes when you file next year? Its a pretty substantial credit - 30% - for solar power equipment purchased for a home this year (and as long as your boat has a bathroom, kitchen and bed it qualifies as a home). Because the credit starts dropping next year I want to get as much done as I can this year. I don't think I can justify an alternator, but the consensus seems to be that the panel, controller, wiring, and batteries can be counted for the credit.

And yup, everything that can be LED is now LED on my boat.
 
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Nov 2, 2017
9
Delphia 37 Bayfield
Marty:

Thanks for taking the time to share your experience. I hadn't seen any responses here, so I started a new thread and posed the same question. There are some very helpful responses in there, including one from Maine Sail. Here's the thread, in case you're interested:

https://forums.sailboatowners.com/index.php?threads/firefly-batteries-and-the-rest-of-the-charging-system.196179/

The consensus - which was really valuable - is that my usage as outlined in my post doesn't warrant Fireflies, or even AGMs, according to Maine Sail. And to properly install the batteries and the right charging system would be pretty expensive, requiring an upgrade to my shore charger and an externally regulated alternator and pulley upgrade. That sounds right - if I understand Maine Sail's extensive writing on the subject of AGMs and their proper care and use.

I think I'm headed down the path of FLAs, and possibly an alternator and pulley upgrade, based on the consensus of my use case. I have everything done for my solar install, but am just waiting for the panel to be sewn to the bimini. I'm anxious to see what I get in terms of Ah from the 160w Renogy panel before I start on the charging system.

Are you planning on taking the solar power equipment credit on your taxes when you file next year? Its a pretty substantial credit - 30% - for solar power equipment purchased for a home this year (and as long as your boat has a bathroom, kitchen and bed it qualifies as a home). Because the credit starts dropping next year I want to get as much done as I can this year. I don't think I can justify an alternator, but the consensus seems to be that the panel, controller, wiring, and batteries can be counted for the credit.

And yup, everything that can be LED is now LED on my boat.
Thanks for the reminder for the solar credit, claimed the initial part last year but the batteries will go on this years!

I saw your other thread after my response to this threas, MaineSail's point about drawing down the Firefly's and their benefits of being in bulk for much more (20%-80% vs. 50%-80%) is very interesting. Honestly on sunny days at anchor I generate more, or very close to it, than I use currently. I would question my ability to truly pull them down to 20% on a typical cycle and the boat is kept in a slip w/ shorepower. Really that just makes the case for only 2 Firefly's! :)

It should be noted that I would more than likely have gone with FLA but without moving the bank I didn't have the height needed for quality FLA's plus they are right under the aft berth. I know off gassing is most unlikely to happen but it still seemed a little close to my head (~ 6 inches!).

I did the alternator primary because on those cold (I have a independent diesel heater which has sizable power draw) days with no sun there was basically no realistic way to charge the bank back up at 15-20amps output. I think mine was ~ $1000-$1200 DIY all said and done, I'd have to add it up but that's against my better judgement to do!
 
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Dec 4, 2018
36
Balboa 27 Denver
Does the Firefly battery still exist? I got on a list for a grp 31 a couple months ago on the Ocean Energy site, and Natta since then. I was also wondering if anyone has had one of these 75 lb monster actually shipped to their house. Maybe I should back up and go to some trojan Gels of similar, at least I have experience with them.
 
Feb 6, 1998
11,258
Canadian Sailcraft 36T Casco Bay, ME
Demand is extremely high for the Firefly's and they are often sold out months in advance. Just check in with Bruce to see where you stand on the list..
 
Dec 4, 2018
36
Balboa 27 Denver
By coincidence, I was contacted by Ocean Energy yesterday after I inquired again and they DO have a shipment in and will be going through their list this week. Good News.