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  #1  
Old 09-13-2010
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AGM Batteries

I recently heard a forum member mention that he thought a lot of people were going to AGM batteries for the wrong reason.

I found that was an interesting comment, what might that reason be.
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Old 09-13-2010
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AGM Batteries are great if you don't like doing battery maintenance, need to stow batteries in odd positions and locations, and have a pretty high amperage charging capability.

They are not a panacea for electrical problems. They have to be charged properly, charged completely at least once a month or so, and are quite expensive compared to wet-cell batteries.

The way most people use their batteries, they really don't provide any real benefit, other than the lack of maintenance.
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Old 09-13-2010
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I agree with Dan's summary, and will add that another benefit is their high acceptance rate and low self-discharge rate.

I disagree with those who say they offer little benefit for most users. I've heard some say that they are best for cruisers. I would say they are great for anyone who can afford them, but especially for non-live-aboard-cruisers.

I say that, because unlike live-aboards or long-term cruisers, most boat owners have to divide their time between home, job, family, etc and boat. Anything that eliminates yet one more maintenance task, and offers better performance to boot, is a welcome alternative and worth a premium.

The low self-discharge rate is especially advantageous to folks who only visit their boats every few weeks and don't have access to charging via shorepower -- for instance, folks who keep their boats on moorings.

We switched a decade ago, and I'll never go back to wet cells.
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Old 09-13-2010
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Wrong reason's that I have seen:

#1 Bought a 200-800 ah bank for their high acceptance rates then fed them with a 100 amp alt and 40 amp shore charger.

#2 Bought them for the "low maintenance" then ran the engine 35 hours a season. Even the worst wet cell on the worst charger won't boil off on 35 engine hours per year.

#3 Bought them for low self discharge rates then left them sitting at 50% - 80% charged after each sail and killed them in three seasons.

#4 Bought them for the claimed "longer life" then found out they were dead in 4 seasons anyway, when his previous wet cells lasted 7.

#5 Bought them to replace wet cells that died a premature death then the AGM's proceeded to do the same because the owner refused to address his/her battery practices.

6# Bought them because they don't give of "gas fumes" when charging. (His previous bank had zero signs of corrosion and in four years had never even taken water. When I opened them up they were still full and load tested at nearly new. Gave that bank to a friend who got two more seasons out of them. The "new" fumeless AGM's died at year five.....)

#7 "The guy at West Marine said they were the best." He then proceeded to fry two stock alternators and finally had to buy a fully gourmet charging system for another 1.3k. Previous wet bank on dumb regulated alt lasted six years and cost $300.00 vs. $1000.00 + $1300.00 alternator regulator installation. $2300.00 vs. $300.00. I'll be surprised if he gets 6 years out of the Deka/WM AGM's (only on year two now)...

I see and work on boats left on moorings, it's Maine, and the only thing I can ascertain is that AGM's do not like to sit discharged as mooring boats often do. I have seen LOTS of expensive AGM banks die before 5 seasons. I also check date codes every time I am at my local battery distributor on the core pallets. The 6 year old AGM core is a rather rare up here while the 6 & 7 year old wets are not all that uncommon on the pallet. Most of the dead AGM date codes are between 4 & 5 years at Dave's shop.

Nearly every boater I know with AGM's has bought them for their ability to take a fast charge then fed them with a diminutive alt that took no advantage of the high acceptance (wrong reason #1). I have personally seen a 100 Ah Lifeline take 85 amps for more than just a few minutes. I have yet to see any boater truly take advantage of the actual acceptance rates on a large bank because you'd need a HUGE alt to do so and small sailboat AUX engines just can't do this.

I replaced four T105's on a Sabre 362 that had lasted 7 years with a 90 amp dumb regulated alt. Boat resided on a mooring with no solar or wind. The Lifeline bank cost over $1400.00 and was flat dead going into the spring of what was to be their fifth season. At the same time we upgraded the batts we did a full gourmet charging system with 150 amp alt, dual pulleys, MC-612 Balmar regulator, temp sensing etc. etc. on and on. He even bought a maintenance charger that was recommended by Lifeline tech support for the off season where they were stored in his 55 degree basement and cycled on and off the charger to keep them at 100% SOC. Total cumulative motor run time over the four previous seasons was just over 400. The bank had never been discharged below 60% SOC during these four seasons as monitored by Link 20. Dead, grave yard dead. Lifelines attitude, not out of the ordinary, try equalizing. He's back to 6V wet cells again, expensive experiment.. This is one I really feel terrible about because at the time I had bought the AGM static hook line and sinker and really pushed this guy towards this set up. I have wracked my brain as to what cased this but there is no answer. Everything was done by the book.

Oh and then their is my buddy who is the head systems tech at a very well respected boat yard here in Maine. He is an ABYC marine electrician, NEMA certified etc. etc. on and on and on. Probabaly one of the best marine guys I know in tems of knowledge. His own bank of AGM's in his own boat lasted three seasons (Deka's). He's gone to gel.

Don't get me wrong, there ARE benefits to them, and if you can truly take advantage of these benefits they can definitely be worth it. Most I see don't truly take advantage of the benefits. If you go AGM try and keep them fully charged as best you can. If on a mooring get solar or wind to augment. If you can afford a $1300.00 bank you should really take care of them. In my opinion and based on the "claims" these banks should have all easily gone 7+ years.

I had planned to go to AGM but I am still with wets because I have been able to live vicarously though many friends and customers AGM trials and tribulations.
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Last edited by Maine Sail; 09-13-2010 at 09:37 PM.
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Old 09-13-2010
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Quote:
Originally Posted by Maine Sail View Post
I had planned to go to AGM but I am still with wets because I have been able to live vicarously though many friends and customers AGM trials and tribulations.
What a great post RC. Who would have thunk. Something new and expensive don't live up to expectations.
Maybe NiCad, Lithium or some such technology will save us some day.

Last edited by davidpm; 09-13-2010 at 09:37 PM.
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Quote:
Originally Posted by davidpm View Post
What a great post RC. Who would have thunk. Something new and expensive don't live up to expectations.
Maybe NiCad, Lithium or some such technology will save us some day.

I think if AGM's are left topped up, like if you are on a dock regularly, they can last as long as wets but I have yet to hear of many success stories where AGM's clearly out lasted good quality deep cycle wets. The original claims were many, many more cycles than wets.

I have only topped up my bank of wets ONCE in the last four seasons, took me all of three minutes. My bank cost me $240.00. The same bank in Lifelines would be about $1000.00. A $760.00 savings for 3 minutes work is a good pay to me...

I find this to be an interesting quote by Trojan Battery. When AGM's first came out the claims were BETTER cycle life than wets..

Quote:
Originally Posted by Trojan Battery
Generally, gel and AGM batteries have about 20% less capacity, cost about two times more, and have a shorter cycle life than comparable flooded lead acid batteries. However, Gel and AGM batteries do not need watering, are safer (no acid spilling out), can be placed in a variety of positions, have a slower self-discharge characteristic, and are more efficient in charging and discharging than flooded batteries (see table below). Gel batteries are more suitable for deep cycling applications whereas AGM batteries are more for light cycling and engine-starting applications.
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Last edited by Maine Sail; 12-06-2010 at 10:47 AM.
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Old 09-14-2010
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This is why I'm using wet cells too. I like my money to stay MY MONEY.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
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—Cpt. Mal Reynolds, Serenity (edited)

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Old 09-14-2010
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We recently replaced our 3 year old 210 AH AGMs with wet Trojans. We discovered that living at anchor, we couldn't get the AGM batteries to 100% as often as they like. The company who made them even replaced all 3 batteries when they died for free, including shipping them to the Keys. After we had problems with the second set, we had had enough and decided to replace them with wet cells.

I think AGMs work great if you have dock access often and can keep the AGMs at 100%. I have met cruisers who haven't had any problems with their AGMs, but I have seen many who experienced the same issues that I did where the AGMs would quit holding about 30-40% of their charge.
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Quote:
Originally Posted by Maine Sail View Post
I think if AGM's are left topped up, like if you are on a dock regularly, they can last as long as wets but I have yet to hear of many success stories where AGM's clearly out lasted good quality deep cycle wets....
MS,

Interesting how different your experience is from ours.

We are on our 8th season with the 2xGrp31 AGMs. Seven of those seasons were on a mooring (for nine months/year), with no solar trickle charge. We have a stock 55 amp, internally regulated Hitachi alternator.

In those eight seasons, aside from a quick visual inspection, I have done absolutely NOTHING to or with the batteries.

Go figure.
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Old 09-14-2010
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Purchased my Lifeline AGM's in 2006. No problems. However, I have a very large solar array and they generally stay fully charged. My experience is similar to John Pollards.

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