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John Blue
The information below is from FMCA 2010 and points out the good things about AGM batteries for RV units. We use them and found the information to be true and they work well in our case. Only down side is higher cost over flood cells. Our plans are to use them into the future years. Drop them in and forget them. This works for me!

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A Better Battery:

Dear RV Doctor:
I think my coach batteries may need to be replaced within the year. I asked my RV dealer whether AGM batteries are a good idea. My motorhome currently has the older flooded-cell-type batteries that came from the factory (two chassis batteries and three house batteries). The answer I got from my dealer was to stick with the technology it came with and not switch to AGM batteries. I have a 2004 Itasca with a three-stage charger. Iíd be interested in your comments and advice.

Answer:
Iím guessing your dealer does not sell absorbed glass mat (AGM) batteries but does sell flooded wet-cell batteries. My advice? Well, Iím a strong proponent of the AGM technology. And since todayís motorhomes are so DC-voltage dependent, Iím also in favor of having as much DC current on board as possible. Following are some arguments for switching to AGM batteries.

First, they are highly resistant to vibration and shock, which is a plus for RV applications when you consider the jostling and bouncing the motorhome does on the road. Their recombinant gases are effective to about 99 percent. What this means is that the hydrogen and oxygen are recombined inside the battery safely within each cell. Have you ever noticed the bubbling and off-gassing of a lead-acid battery while under a charge? Most AGM batteries vent hydrogen vapors at less than 2 percent, where 4.1 percent hydrogen vapor is needed to support flammability in the air.

The inherently low internal resistance of an AGM battery is another welcomed benefit to RVers who store their motorhomes part of the year. According to one maker, during storage, the self-discharge rate of an AGM battery is three to 10 times less than a gel battery and almost 50 times less than a typical flooded lead-acid battery. The reason is because the electrolyte is not liquefied, but rather absorbed into the floss-like glass matting.

AGM batteries also deliver and receive current much faster and at the higher rates available today. Your three-stage charger will suffice nicely and adapt well for AGM batteries. As an example, AGM batteries can be charged 10 times faster than a same-rated gel battery and five times as fast as a like-sized flooded lead-acid battery. Because AGM battery technology permits more positive plate material to be saturated by the absorbed mats in each cell, there is an automatic increase in the batteryís capacity in virtually every area.

More life cycles, reduced internal resistances, higher amp-hour rating, more reserve capacity, and greater depth of discharge cycles are some of the improvements when compared to other types of sealed lead-acid batteries.

As you can see, I do like AGM batteries. So, in my opinion, if your wallet can endure the outlay and you consider yourself a serious RVer, then you should consider the upgrade when itís time to replace your existing batteries.

RCDCTN
Can you comment on the cost comparrison of the two battery types?
Texasrvers
John,

Good article. I appreciated the information.



RCDCTN,

We just bought 2 AGM's at the first of December, and we spent about $100 more per battery than the price quoted for the regular type batteries. The AGM's were about $350 each. I'm sure a lot depends on where you purchase the batteries, and I'm equally sure there are deals to be had if you want to take the time to do the looking.

If you are interested in AGM's you might also read the thread in this forum titled "Learning About Batteries." It is near the bottom of the first page of topics.

TX
Florida Native
My gel batteries are on their last legs and I have decided on AGM batteries. I need two group 29 with as much amp hours as I can get. John, where did you buy yours. I am not too far from Brandon. I have looked at several brands and they are suposedly sold in Tampa, plus you can get them shipped in UPS. I am going on a 3 month trip in April and need to just go ahead and buy them.
John Blue
RCDCTN,

We have only use Gel and AGM batteries. We have two 8G8D AGM's in place at $880 for the two with tax and all. Gel cost a little more from most places and flood cells cost about 2/3 less over AGM. The price is also driven by companies who sells them. Lot of different ones on the market. Lifeline batteries out of CA are very good but very high as well. Shop around and check your prices. Remember if you order them the shipping would add up in cost. I buy them here in Tampa at a local battery shop. Weight is 192 lbs per battery.
pianotuna
Hi John,

Nice article.

No battery is perfect. I have found some concerns with AGM batteries.

The Bad:

1. They do want to be charged to 100% as often as is possible. (This is very like regular flooded cells). They are subject to concentration and saturation stratification, which may lead to negative plate sulphation.

2. They may be subject to internal corrosion greater than that in flooded cells. There is no reason given in the article I read--but I can guess it may be due to the oxygen which in a flood cell dissipates into the air but in an AGM is held inside so it can recombine with hydrogen.

3. Charging voltage on stock converters may not be correct--but with the new generation of "smart" converters it's no great task to set the voltage correctly.

4. They appear to be less tolerant of overcharging especially at voltages that are higher than recommended by the maker.

5. The cost per amp-hour is higher and even though they do, under ideal conditions, allow more cycles, the extra life span does not equalize the cost.

The good:

1. They can be rapid charged at a c/1 rate.

2. They have low internal resistance, and so can put out lots of amps quickly.

3. They can be mounted in any position.

4. The "finish" charge starts at nearer full capacity than flooded cells.

5. They are nearly maintenance free.

6. There are almost no differences between AGM's in a twelve volt format vs a six volt format.

7. The self discharge rate is outstanding!
Florida Native
QUOTE(John Blue @ Jan 7 2010, 09:53 PM) *

RCDCTN,

I buy them here in Tampa at a local battery shop. Weight is 192 lbs per battery.



What is the name of the battery shop. We are 90 miles away from Tampa and I might go over and make a trip out of it. I looked on the internet and couldn't narrow it down. Thanks a lot John.
John Blue
Lindsay,

We have a number of shops here in Tampa and other places around here so I will list what is outside Tampa as well. Prices are up and down so call around before you pick a shop. Remember to take in the old core or they will add on more cost. Shops are the large ones and turn over batteries at a high rate so you get batteries that have not sit around long. I have picked up T-105s right off the truck that moved them from CA to Tampa.

Posey Power Batteries 813-621-6402 Tampa

Interstate Batteries 813-932-0108 Tampa

Utility Battery Co. 813-621-8261 Tampa

Taylor & Crowe Battery 863-616-1538 Lakeland

American Battery Company 863-616-1550 Lakeland

Florida Native
Thanks a lot. I have confinced the wife which is harder than actually paying the higher price.

Thanks again
pianotuna
Hi Lindsay,

Here is a low cost source for AGM's that I stumbled upon today:

http://www.thesolar.biz/AGM_Batteries.htm
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