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Kiwi · 12-20-2015, 08:03 PM

AGM (Absorbed Glass Mat) Batteries

A newer type of sealed battery uses "Absorbed Glass Mats", or AGM between the plates. This is a very fine fiber Boron-Silicate glass mat. These type of batteries have all the advantages of gelled, but can take much more abuse. We sell the Concorde (and Lifeline, made by Concorde) AGM batteries. These are also called "starved electrolyte", as the mat is about 95% saturated rather than fully soaked. That also means that they will not leak acid even if broken.

AGM batteries have several advantages over both gelled and flooded, at about the same cost as gelled:

Since all the electrolyte (acid) is contained in the glass mats, they cannot spill, even if broken. This also means that since they are non-hazardous, the shipping costs are lower. In addition, since there is no liquid to freeze and expand, they are practically immune from freezing damage.

Nearly all AGM batteries are "recombinant" - what that means is that the Oxygen and Hydrogen recombine INSIDE the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost.

The charging voltages are the same as for any standard battery - no need for any special adjustments or problems with incompatible chargers or charge controls. And, since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents. The Concorde (and most AGM) batteries have no charge or discharge current limits.

AGM's have a very low self-discharge - from 1% to 3% per month is usual. This means that they can sit in storage for much longer periods without charging than standard batteries. The Concorde batteries can be almost fully recharged (95% or better) even after 30 days of being totally discharged.

AGM's do not have any liquid to spill, and even under severe overcharge conditions hydrogen emission is far below the 4% max specified for aircraft and enclosed spaces. The plates in AGM's are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery.

Even with all the advantages listed above, there is still a place for the standard flooded deep cycle battery. AGM's will cost about 1.5 to 2 times as much as flooded batteries of the same capacity. In many installations, where the batteries are set in an area where you don't have to worry about fumes or leakage, a standard or industrial deep cycle is a better economic choice. AGM batteries main advantages are no maintenance, completely sealed against fumes, Hydrogen, or leakage, non-spilling even if they are broken, and can survive most freezes. Not everyone needs these features.

w2drfg · 12-21-2015, 03:22 AM

@Kiwi
Nice wtiteup on AGM batteries. What are the negatives and how long do they last before having to replace them? What kind of warranty do they carry. Where does a person get them serviced while camping?

Reed Cundiff · 12-21-2015, 07:51 AM

We had AGM batteries on our previous 5th wheel. We had them for five years and they were still going strong. Would highly recommend their use.

Reed and Elaine

montyhp · 12-29-2015, 02:36 PM

If money and weight are no object, go with agm 6v golf cart batteries. Contrary to earlier comments, these batteries have much thicker plates than ordinary batteries and should last significantly longer.

Mr_D · 12-29-2015, 02:51 PM

I found that 8D AGM's were well over $500 each and some were up to over $700 each. Yep, they have advantages like faster charging but the last wet cell's I had lasted 10 years. When I need new house batteries I'll go to Sam's Club or Costco and get GC-2's at less than $200 a pair (need a pair to replace one 8D).

1bigmess · 12-29-2015, 02:54 PM

The costco GC2's were about $80 each when I was looking, but the capacity wasn't much.

Mr_D · 12-29-2015, 03:08 PM

Quote:

Originally Posted by 1bigmess

The costco GC2's were about $80 each when I was looking, but the capacity wasn't much.

In pairs they are equivalent to an 8D AGM in amp hours and way less than half the price of an 8D AGM. But I will have to have more connection cables made and they aren't cheap either!

Kiwi · 12-30-2015, 07:41 AM

Quote:

Originally Posted by ksmith

@Kiwi
Nice wtiteup on AGM batteries. What are the negatives and how long do they last before having to replace them? What kind of warranty do they carry. Where does a person get them serviced while camping?

What service?? They are sealed. Mine are Interstate AGM. They have service centers in all major cities and a bazillion shops that carry them as dealers. I had them in my diesel pusher that was 7 years old when I sold it. Batteries still going strong.

Lots of lead acid battery failure is due to owner maintenance failure. Water gets low, batteries overheat and buckle the plates. A sealed maintenance free battery is more than just free from worry, it is free from owner induced damage.

okcnewbie · 12-30-2015, 07:50 AM

Quote:

Originally Posted by Kiwi

..... it is free from owner induced damage.

.....at least the type of damage from not keeping the plates covered with water.

twinboat · 12-30-2015, 08:32 AM

That " leaving them sit in storage dead " damage is another story.

Smitty77 · 12-30-2015, 11:33 AM

OP - If you are a frequent boondocker, and want to have some added insurance with reserve capacity, going to AGM's will for sure provide more peace of mind.

One other advantage I don't think I saw in this thread, is AGM's recharge at a faster rate then wet batteries. So on partial shading days, that can be an advantage.

I like the idea of selling your new batteries on Craigslist, and making the move now to whatever battery you plan to use for the long haul. (Nothing wrong with wet, as mentioned they are tried and true.)

Only you can decide if the cost of AGM is warranted for your usage.

Best,
Smitty

twinboat · 12-30-2015, 12:03 PM

Quote:

Originally Posted by Smitty77

OP - If you are a frequent boondocker, and want to have some added insurance with reserve capacity, going to AGM's will for sure provide more peace of mind.

One other advantage I don't think I saw in this thread, is AGM's recharge at a faster rate then wet batteries. So on partial shading days, that can be an advantage.

I like the idea of selling your new batteries on Craigslist, and making the move now to whatever battery you plan to use for the long haul. (Nothing wrong with wet, as mentioned they are tried and true.)

Only you can decide if the cost of AGM is warranted for your usage.

Best,
Smitty

When I have compared AGM with Wet cell batteries, size for size, I don't see a noticable difference in AH capacity.

They claim you can draw them down below 50% but also recommend that you don't, if you want long life. Same with Wet cell batteries.

Recharging at a faster rate takes a higher charging rate.

IMO, Most solar systems are not designed for a high enough rate to make much of a difference.

A 400AH AGM bank can be charged at 100 amps. That will take a 1200 + watt array to produce.

Smitty77 · 12-30-2015, 01:00 PM

Quote:

Originally Posted by twinboat

When I have compared AGM with Wet cell batteries, size for size, I don't see a noticable difference in AH capacity.

They claim you can draw them down below 50% but also recommend that you don't, if you want long life. Same with Wet cell batteries.

Recharging at a faster rate takes a higher charging rate.

IMO, Most solar systems are not designed for a high enough rate to make much of a difference.

A 400AH AGM bank can be charged at 100 amps. That will take a 1200 + watt array to produce.

Hey Twinboat - Agree with all of your comments

!

I do have 1200W of Solar Panels, and I do have the MidNite Classic 150 which is able to not only route AGM charge levels to the batteries, but also specifically the Lifeline AGM recommended levels of power.

I do feel that higher quality AGM's, rated with the same AH of say a wholesale sold GC battery of the same rating, will provide added insurance over the life of the battery. I know you know this, as I've always found your posts to be both informative and knowledge based. It is all about the battery rating of life cycles. (Very hard to find this spec on the warehouse GC batteries.) I followed the advice of another board member from a different forum, from back in 2004 timeframe. His recommendation was to:
-Figure out your AH needs
-Add about 10-15% to this for contingency and added goodies down the road
-Size you house battery bank to support that amount of AH usage, and still be between 70-75% of SOC in the AM
-Don't skimp on the quality of the battery you use, maintain them well, and do your best to never abuse them by dropping below 50% SOC.
-Never go more then two days with out doing a full 100% SOC recharge. So two days back to 95%, and then the third get it back to 100%.
-Be sure to right size your cables

His view, and now mine as I have adopted it and believe in it, is that you never know what might happen on a trip. Having reserve AH capacity, and the capability when needed to recharge it properly. Give you and edge on safety.

Same thing can be said on keeping your water supply no lower then 50%, and always drive on the top half of your tank.

Good example of reasons why, is what we are seeing in the weather front these last few weeks. Freeways shut down, motorist stranded at times. Or say your in a region where earthquakes or forrest fires are prone. Or even another major attack of smoking on the US mainlands. Stuff happens, and paying a bit more on equipment sizing and quality, can pay dividends in the long run.

Sure not trying to preach, and of course not directed to you.... And again, nothing wrong with wet batteries, tried and true. But IMO, same comments on different levels of quality within the wet cells is a reality.

And, opinions vary - and that is OK!!

(Not intended as a response to you, or anyone else in this thread. But quite often batteries threads get into a wet vs AGM, and many times some members feels that only their way of thinking is the right way. Same thing on tires, where the Michelin users can get beaten on by the Michelin haters. --- Heck, this board provides so much overall info, where everyone pitches in and does their best to help each other on so many areas. I feel thankful that the number of posts that go 'sideways' are so low...) Now, onto something more important 'Chevy vs Ford' and the always fun 'Dino vs Syn'

!

Best to you, and all,
Smitty

Scottybdivin · 12-31-2015, 07:51 AM

I recently went through the dilemma of choosing wet vs AGM. I was also not able to find any technical information about the warehouse GC-2's. However, I did find the spec sheets on both Trojan T-105's and Lifeline AGM's. All things being equal, the T-105's have a higher charge cycle rating than do the Lifelines. My battery compartment is pretty much open-aired with a louvered compartment door, so ventilation is not an issue. It really boils down to how much you are willing to pay for the convenience of not having to add water or worry about corrosion. I bought 8 T-105's for $1189 and the quote for Lifeline AGM's was $2392. The other way I look at it is, having to check the water once a month will force me to inspect all the cables and connections. If I had AGM's, maybe I would forget about it.