AGM vs Flooded - Fiberglass RV


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Old 09-07-2016, 12:18 PM   #1
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AGM vs Flooded

My old battery is showing extreme decrease in capacity. I "load tested" it by plugging in a 12v cooler that uses about 4 amps, and it lasted < 4 hours, it is a 70amp battery.

So I have read everything that I can about battery technology, and concluded that the 2 most popular deep cycle battery types are AGM and Flooded (Li-ion cells are still price prohibitive and may have heat issues).

Below are the advantages of AGM batteries that I can gathered:

1) No maintenance -- no need for topping up fluid at all, compared to Flooded type which will need to be watered (even the ones that advertised as "maintenance free"

2) Low self discharge -- the charge will hold for over a year, which means no need to remove it and put it on a maintenance charger

3) Faster charge time -- I keep hearing this but I haven't seen any real statistics on it. How much faster are we talking about? AGM still needs a 3 or 4 stage charger so the last 10% of charging will be painfully slow still?

Other than the above 3 advantages, the two types of batteries have the same characteristics where discharging more that 50% will harm the battery and cause sulfation.

Do I have a good understanding? If so, it seems like if I am willing to do the maintenance work, flooded batteries are a better deal at essentially half the price? Any other gaps in my analysis?

Thanks everyone!
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Old 09-07-2016, 12:46 PM   #2
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Add to your list that AGM batteries do not off-gas so they can be placed inside the coach without extensive venting. Also, I believe, they can be oriented in any position, do not need to be kept upright.

Correction:
Well, in spite of hearing several folks tout the fact that AGM batteries do not need venting, Mike (Civilguy) kindly corrected me on this point. Apparently, in normal operations, an AGM battery does not off-gas hydrogen. It is possible, however, for a malfunctioning charger to cause an internal safety valve in the battery to release hydrogen gas, which is very explosive. For this reason, virtually all the manufacturers and others in the know suggest and/or require that ALL batteries should be vented to the outside.
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Old 09-07-2016, 12:52 PM   #3
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AGM can be discharged to a lower level without battery damage.
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Old 09-07-2016, 12:58 PM   #4
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Quote:
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AGM can be discharged to a lower level without battery damage.
This is interesting, I have actually seen both 50% and 80% being thrown around and got a little confused. I think if I AGM can indeed be discharged to 80%, then it may be worth the higher price.
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Old 09-07-2016, 01:26 PM   #5
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BU-201a: Absorbent Glass Mat (AGM)

Learn what differentiate AGM from other lead acid battery types

AGM technology became popular in the early 1980s as a sealed lead acid battery for military aircraft, vehicles and UPS to reduce weight and improve reliability. The sulfuric acid is absorbed by a very fine fiberglass mat, making the battery spill-proof. This enables shipment without hazardous material restrictions. The plates can be made flat to resemble a standard flooded lead acid pack in a rectangular case; they can also be wound into a cylindrical cell.

AGM has very low internal resistance, is capable to deliver high currents on demand and offers a relatively long service life, even when deep cycled. AGM is maintenance free, provides good electrical reliability and is lighter than the flooded lead acid type. While regular lead acid batteries need a topping charge every six months to prevent the buildup of sulfation, AGM batteries are less prone to sulfation and can sit in storage for longer before a charge becomes necessary. The battery stands up well to low temperatures and has a low self-discharge.

The leading advantages of AGM are a charge that is up to five times faster than the flooded version, and the ability to deep cycle. AGM offers a depth-of-discharge of 80 percent; the flooded, on the other hand, is specified at 50 percent DoD to attain the same cycle life. The negatives are slightly lower specific energy and higher manufacturing costs than the flooded.

Most AGM batteries are mid-sized and range from 30 to 100Ah. They are commonly built to size and are found in high-end vehicles to run power-hungry accessories such as heated seats, steering wheels, mirrors and windshields. NASCAR and other auto racing leagues choose AGM products because they are vibration resistant.

AGM is the preferred battery for upscale motorcycles. Being sealed, AGM reduces acid spilling in an accident, lowers the weight for the same performance and allows installation at odd angles. Because of good performance at cold temperatures, AGM batteries are also used for marine, motor home and robotic applications.

AGM is making inroads into the start-stop function of cars. The classic flooded type is simply not robust enough and repeated cycling causes a sharp capacity fade after only two years of use. (See BU-806a: Heat, Loading and Battery Life.)

As with all gelled and sealed units, AGM batteries are sensitive to overcharging. A charge to 2.40V/cell (and higher) is fine; however, the float charge should be reduced to between 2.25 and 2.30V/cell (summer temperatures may require lower voltages). Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell); a direct replacement with a sealed unit could overcharge the battery on a long drive. (See BU-403: Charging Lead Acid.)

AGM and other sealed batteries do not like heat and should be installed away from the engine compartment. Manufacturers recommend halting charge if the battery core reaches 49°C (120°F). Table 1 spells out the advantages and limitations of AGM.



Advantages

Spill-proof through acid encapsulation in matting technology

High specific power, low internal resistance, responsive to load

Up to 5 times faster charge than with flooded technology

Better cycle life than with flooded systems

Water retention (oxygen and hydrogen combine to produce water)

Vibration resistance due to sandwich construction

Stands up well to cold temperature

Less prone to sulfation if not regularly topping charged


Limitations

Higher manufacturing cost than flooded (but cheaper than gel)

Sensitive to overcharging (gel has tighter tolerances than AGM)

Capacity has gradual decline (gel has a performance dome)

Low specific energy

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

Not environmentally friendly (has less electrolyte and lead than flooded)


Table 1: Advantages and limitations of AGM.


Advantages

Spill-proof through acid encapsulation in matting technology

High specific power, low internal resistance, responsive to load

Up to 5 times faster charge than with flooded technology

Better cycle life than with flooded systems

Water retention (oxygen and hydrogen combine to produce water)

Vibration resistance due to sandwich construction

Stands up well to cold temperature

Less prone to sulfation if not regularly topping charged


Limitations

Higher manufacturing cost than flooded (but cheaper than gel)

Sensitive to overcharging (gel has tighter tolerances than AGM)

Capacity has gradual decline (gel has a performance dome)


Additional information on Batteries:

A chemical reaction is taking place where electrons are passing through a substance. The amount of out gassing will vary from substance to substance, but it will still be happening.

Be aware and beware of how the physical geometry relates to any possible leakage of internal components of a battery.
Low specific energy

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

Not environmentally friendly (has less electrolyte and lead than flooded) but there is still an electrolyte.
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Old 09-07-2016, 01:35 PM   #6
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I think it depends on your charging equipment and charging strategy. If you have the proper charging equipment and store your trailer someplace that it can be plugged in 24-7 a standard flooded cell battery works well. If you store your trailer in a lot with no power for months on end an agm battery technology makes allot of sense wired and vented to be inside your trailer. Allot better storage and less likely to walk off with the undesirables.

I am finding it is harder to get good lead acid batteries since the mergers of battery companies and for the most part now being built in Mexico. The price of the batteries between the AGM and flooded cell are getting much closer these days unless you want a 2 year life cycle battery.

There is nothing worse than having a long winter season and having to maintain a bunch of batteries from all your toys. Removing them to a warm place and keeping them properly charged. Sooner or later you neglect them and murder your batteries.
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Old 09-07-2016, 01:48 PM   #7
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I can buy a 6V 225 Ah AGM here in town for $250 CAD. Not bad at all.

https://www.solarwholesaler.ca/produ...r-agm-battery/
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Old 09-07-2016, 01:58 PM   #8
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Real decent price! Too bad the drive to pick it up will negate all the savings for me

Quote:
Originally Posted by Jim Bennett View Post
I can buy a 6V 225 Ah AGM here in town for $250 CAD. Not bad at all.

https://www.solarwholesaler.ca/produ...r-agm-battery/
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Old 09-07-2016, 03:10 PM   #9
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I'd prefer to replace $100 battery every 3 years rather than $250 battery every 5 years...
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Old 09-07-2016, 03:52 PM   #10
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Originally Posted by sokhapkin View Post
I'd prefer to replace $100 battery every 3 years rather than $250 battery every 5 years...
An AGM will last a lot more than 5 years. Besides, where would you ever get a good quality $100 battery, even assuming you mean in USD (the one I posted is $250 CAD, which is only $194 USD). Plus, there is a lot more advantages than just the price. I researched it a lot before deciding that is the way I am going to go.
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Old 09-07-2016, 04:21 PM   #11
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Comments from Absorbent Glass Mat (AGM) Battery Information - Battery University :

Jean L Genibrel wrote:
Speaking from experience with flooded, gel and AGM batteries I can safely say that AGM batteries do not have better cycle life than flooded and certainly not that of gel. The only advantage to AGM batteries is that the seller can claim high Cold Cranking Amperage, which in the real world is pretty much meaningless but those big numbers appeal to the buying public. Keep in mid that in order to create an AGM battery the plates must be very thin in comparison to a flooded battery or a gel one. This type of construction allows for higher CCAs but lower cycling ability. real cycling should be undertaken to 10v not just 12.6 or12.7.


On September 16, 2012 at 11:13pm
jon sansfras wrote:
AGM can come in starting and deep cycle like any other battery. They’re not inherently more capable of deep discharge. I’m finding alot of just plain wrong info on this site.
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Old 09-07-2016, 05:05 PM   #12
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Quote:
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I’m finding alot of just plain wrong info on this site.
Welcome to the world of internet forums.
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Old 09-07-2016, 05:10 PM   #13
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Quote:
Originally Posted by sokhapkin View Post
Comments from ....
Exactly that, just user comments. You and I could post there, yet that does not make us experts.

I don't disagree that one should not just take any article on the web for being absolutely true. One must do lots of research and only then will find the truth (or at least closer to it ).
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Old 09-07-2016, 05:49 PM   #14
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I am also curious about the "5 times faster charge" of an AGM vs. Flooded for the deep cycle batteries. Is the AGM more efficient at storing the available amps supplied to it or does that only mean you can crank up the amps and charge it faster? How would this work out with a solar system on a cloudy day with marginal output? All things being equal would the AGM still charge slightly faster than flooded?
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