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Old 21-02-2021, 16:47   #1
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Why are so many in Love with AGM's

I have had nothing but problems with AGM batteries, from early failure after 18 months in lawn equipment, failure after 24 months in road vehicles (seems the batteries have insider knowledge of the warranty expiration date), to full blown melt-down and fire at cell tower standy power cabinets. Never had theses issues with lead-acid batteries. Is it because the AGM's are sealed and cannot gas-off?
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Old 21-02-2021, 17:04   #2
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Re: Why are so many in Love with AGM's

AGM are lead acid batteries. I have never had or heard of the problems you describe with Absorbed Glass Mat lead-acid batteries.
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Old 21-02-2021, 17:07   #3
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Re: Why are so many in Love with AGM's

AGMs aren't as abuse tolerant as flooded lead acid. So they're not necessarily better unless you need their specific advantages. And they're more expensive. But if cared for properly, they last just fine.
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Old 21-02-2021, 17:34   #4
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Re: Why are so many in Love with AGM's

As far as I'm concerned the cost/benefit ratio favors the flooded lead acid. Experienced everything noted except the fire.

Have no explanation for their popularity.
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Old 21-02-2021, 17:34   #5
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Re: Why are so many in Love with AGM's

I had early AGM failures on a motor cycle until increasing the output voltage of the regulator from 13.8 to 14.6 V.

Boat batteries are 3 years old and performing just fine.

Starting battery is cyclic wound.
House batteries are cheapest chinese flat plates I could find. ($1.00 / Ah)

Bulk and Absorb at 14.5 V. Float at 13.5 V. Storage at 13.2 V with current in and load out.

12.8 V alarm for low voltage - try not to drop below 12 V to often.

Money spent on charging systems is money saved on batteries.

AGMs are reliable, robust and not expensive.
The low maintenance, non venting, non spilling (even upside down) qualities increase installation options including passenger compartments.

The required improvements to charging systems over FLA are minor.

I like them because I'm cheap and lazy.
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Old 21-02-2021, 17:45   #6
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Re: Why are so many in Love with AGM's

I use a pair of Firefly carbon foam AGMs, three years old and operating as advertised. I have no complaints as of yet.

Fair winds,
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Old 21-02-2021, 18:01   #7
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Re: Why are so many in Love with AGM's

In 2007, I installed ten vision AGM 60Ah 12 V batteries - parallel organized in two battery banks in our 34' sailboat with a small solar cell on the top of the the downturn hatch ... (I'm not sure of the correct terminology ...).
The capacity of the two battery banks is dimensioned in order to be able to sail for three consecutive days and nights (72 hours) running the cooling compressor, instruments, VHF, AIS, two plotters, autopilot, electric winches, pumps, Thinkpad PC, mobile units, router, lights, radio, etc. ... without having to charge the batteries from the engines generator or shore power.
During this period, we have been sailing and anchoring a lot in the Norwegian, Swedish, Danish and Finnish waters and archipelago during the summer period.
I'm planning to invest in new AGM-batteries this year ... ...
I would add, I have tried to take good care of the batteries, and have been very satisfied with my AGM batteries, that are placed under the berth bottom i.e. difficult to access or service ...
I did consider LiFePo4 technology, but did not want to change existing charging system, and I'm a pretty old and conservative sailor ...
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Old 21-02-2021, 18:10   #8
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Re: Why are so many in Love with AGM's

My 1st set of Lifeline group 31's lasted 8 years, I then sold them in Mexico for $100 each, they were still fine but I replaced them with Lifeline group31+ as I didn't want a battery hassle in Polynesia.
I suspect the newer set will last me at least 10 years.


No clue about regular lead acid.
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Old 21-02-2021, 18:19   #9
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Re: Why are so many in Love with AGM's

I have 2 mastervolt 200 AH in my boat. 2 years old. With the charger off they always drop from 13.2 to 12.1 in 2 days unattended . I dont think there is a leak as 12 volt panel is turned off. Is this drop in volts unusual??
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Old 21-02-2021, 18:22   #10
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Re: Why are so many in Love with AGM's

I would say the love for Lifepo is greater nowadays !
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Old 21-02-2021, 20:44   #11
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Re: Why are so many in Love with AGM's

LiFePo and AGM are suited for entirely different situations.

As LiFePo degrade quickly when kept fully charged while AGM degrade when stored uncharged, I would not consider LiFePo a viable option in my current situation as my boat stay in its dock on shorepower 90% of the time.

When I go cruising, and live on solar and wind with a occational full charge, I will consider Lifepo.

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Old 21-02-2021, 22:33   #12
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Re: Why are so many in Love with AGM's

I have 5 Westmarine group 31....one for starter and 4 for house since 2015. Have not had any problems. They are convenient since the sit in the aft berth and need no special housing as well as maintenance free. It is a good fit in my
case.

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Old 21-02-2021, 22:52   #13
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Re: Why are so many in Love with AGM's

For deep cycle use cost favors traction or golfcart FLA over AGM by at least 2:1.

AGM really need to be fully charged most days, i.e. 6d/week.
They need to be charged at relatively high C. 0.2C at minimum, 0.3-0.4 better. Unless they are almost never discharged very far, below 80% let’s say.

So a boat with a really big bank subject to moderate daily draw will do fine.

If you are discharging to 50% 2-4 time per week then you need a generator or big alternator or the batteries will suffer in the long run.

Carbon foam is AGM and is not as picky about getting to 100% daily but it still wants to be charged at higher C than FLAs or Gels.

For a boat that wants to primarily rely on wind and sun for recharging and only has room for a moderate sized bank then FLAs are the way to go.

If you have moderate daily draw and an oversized bank the AGMs are still fine.
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Old 21-02-2021, 23:10   #14
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Re: Why are so many in Love with AGM's

Quote:
Originally Posted by geoleo View Post
I have 2 mastervolt 200 AH in my boat. 2 years old. With the charger off they always drop from 13.2 to 12.1 in 2 days unattended . I dont think there is a leak as 12 volt panel is turned off. Is this drop in volts unusual??

I'm no electrical expert but that voltage drop sounds like you have a big leak assuming your bilge pump isnt running a lot or there is another item left on. You need to put a clampmeter on your battery cable when battery switch is off. If there is a spark when you pull battery cable off battery terminal when everything is off you have a problem that needs to be fixed asap assuming you want good battery life. I see Wotname is online so you might get a better post.
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Old 21-02-2021, 23:48   #15
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Re: Why are so many in Love with AGM's

8 x 220ah yum cha agm's nearing 5 years old now.
Still never get below 80% SOC (20% used) and solar has them at 100% by midday most days.
Cheap, about 1/4 of the price of lp4.
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