# AGM batteries



## PotPie (Jan 23, 2013)

I get these for free from fire alarm service folk.
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. 
I use the AGM's for the 12 volt tv and lights for when the power is down.


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## -JohnD- (Sep 16, 2012)

Might be a dumb question but do you know how they compare to deep-cycle marine battery's?


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## cowboyhermit (Nov 10, 2012)

Deep cycle marine batteries are sometimes AGM. And there are non-deep cycle batteries (automotive) that are AGM.
Deep cycle marine batteries are typically just sealed lead acid though, they often are critcized, especially ones also designed for starting. I have found them to be not exceptionally good or bad, just like rv batteries.


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## bunkerbob (Sep 29, 2009)

I use 8 AGM batteries in the "pit"(shelter) for power, both 12vdc and to the inverter. These are especially good in the enclosed area do to their very, very low off-gassing characteristics. 
I charge them with both the power from our off-grid home power and two 100watt solar panels via a MX60 charge controller.
In my off-grid system I use 40 T-105's.

BB


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## Fn/Form (Nov 6, 2008)

PotPie said:


> I get these for free from fire alarm service folk...


Are you sure they are AGMs? All of the batteries used for fire/security panel backup in my locale are SLAs, not AGM.

A manufacturer/model number would help you determine if you have any doubts.


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## PotPie (Jan 23, 2013)

Fn/Form said:


> Are you sure they are AGMs? All of the batteries used for fire/security panel backup in my locale are SLAs, not AGM.
> 
> A manufacturer/model number would help you determine if you have any doubts.


True most are SLA I dont know what the AGM's are used for, but I got them from the guy that replaced our fire system. I also got some SLA,s from him.


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## jsriley5 (Sep 22, 2012)

They're sending me to maybe get outfited with a scooter (yay yard sales) I intend to ask how often they swap batteries and what they do with the old ones  being VA I imagine they have to get rid of them a certain way but it can't hurt to ask.


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## wolfer (Jan 25, 2012)

I purchased my 4 group 31 agm house batteries for my motorhome from a company in Denver who services ambulance,fire trucks and police cars for the city. He is an expert on inverters and replaces batteries with agm in all the city and county rigs.


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