AGM or Wet Cell

[rorr1821]

My original house and engine batteries are seven year old, but are still working find. However, as proactive move I want to replace both house and engine batteries before I have a problem.

Currently I have 4 deep cycle 6 volt house batteries and 2 engine batteries 12 volt. Both banks are wet cell. I have a Magnum Energy pure sine wave charger/inverter, magnum battery/combiner monitor system and power pulse battery maintenance system. I also have a residential refrigerator which put little extra requirement on the system.

I am looking at Sam's Club batteries at a Mississippi store which are branded as Duracell but are made by East Penn Battery Company in PA. The same company that makes Deka brand batteries. Sam's has both AGM and wet cell batteries. As a side note batteries sold by Sam's West of the Mississippi are made by another company (Johnson Control ??) and are branded Energizer.

I have had good service from the wet cell batteries, but they do have a higher level maintenance requirement. Which bring me to the AGM batteries which seem to require little to no maintenance. However, the AGM is rated about 40 A/H less (190 A/H) than the wet cell batteries (230 A/H) sold at Sam's and the AGM cost is about 60% more than wet cell.

I have been told that AGM batteries charge quicker than wet cell. Does anyone know if this is correct? If a person is willing to deal with the maintenance requirements of wet cell butteries are there other advantages to AGM? Do AGM last longer? Do AGM batteries perform differentially even though they are rated at a lower A/H?

Which ever way I go I will need to be 100% AGM or wet cell because my charger/inverter would need to be set accordingly for both battery banks.

Comments/thoughts are welcome.

[dickandlois]

nor1821.

I do not consider myself an expert regarding the AGM style batteries.

They do not require adding water, That fact means that there is also no problem with acid damage to the terminal connections, often last 10 years or more.

The primary down side is, your charger needs to be programmable to properly charge them and if they are over charged (top high a volt) and the water in the cells, if lost, can not be replaced.

The difference in the amp hr. rating is not as big a problem with the advent of LED lighting. Lighting is / was the biggest continuous load.

Home style refrigerators in coaches often require adding 2 to 4 more batteries and one seldom uses a convection / microwave using the inverter foe extended periods of time with out running the generator.

A new all electric coach and all bets are off. IMHO!

Rich.

[wolfe10]

Your inverter/charger is not an issue-- it has algorithms for properly charging either wet cell or AGM. Merely a matter of programming it.

Advantages of AGM are:

Faster charging (only important if you dry camp and have generator run time dedicated to recharging). This would be more important for you with a residential refrigerator if you dry camp. When on shore power, it really doesn't matter if they take an additional hour to charge. The faster charge rate is due to lower internal resistance. This allows the faster recharge without generating unwanted/harmful heat.

No maintenance and no out-gassing unless severely overcharged.

I suspect that as with wet cell batteries there are some differences in quality. I am quite familiar with Lifeline Batteries. Were introduced to them on our sail boat decades ago. They ARE high quality and stood up well for many years on the severe duty found on our long cruises. I have no first hand information on the AGM's Sams Club sells.

[rorr1821]

I appreciate the feedback. The AGM's definitely have an advantage with low maintenance, and the quicker re-charge rate is nice but not a deal breaker. It really comes down to cost and quality. Lifeline Batteries are a proven product but their cost is even greater than the AGM's at Sam's Club. My gut tells me the wet cell batteries at Sam's are probably as good as any on the market but not I am sure about the AGM's. After considering previous information and that which was provided at this forum I believe I will stick with wet cell batteries. Thanks.

[Cruzer]

First of all, your house battery bank and chassis battery bank are two separate items. You don't have to go all AGM or all flooded. I have a mix of AGM house batteries and flooded chassis batteries in our coach and am a big fan of AGMs. Your inverter-charger will be set for ther house batteries, which is what take the charge. Your chassis batteries aren't handled by the inverter-charger unless you have a Trick-L-Start or BatteryMinder installed. Either way, those small charges won't negatively impact your flooded chassis batteries if you have AGM house batteries.

AGM batteries have a number of benefits over flooded. The downside is that they cost more so it's always a decision as to whether yopur particular usage justifies the extra expense. In the case of engine starting batteries, that's pretty hard to justify. But in the house section, that's another story.

As previously mentioned, AGMs charge faster due to less internal resistance. That can be a benefit in certain situations. They don't outgas like flooded batteries do so the terminals and connections don't get the corrosion that you get from the sulfuric acid vapors present in flooded batteries nor do they have the venting requirements of flooded batteries because their hydrogen output is minuscule at best. That gives you a wider choice of where to locate them.

Batteries also have a recommendation to never discharge below 50% or else it takes a toll on their longevity. In reality, it's not the 50% that's the cutoff point. It's the voltage drop at 11.8 volts. On a flooded battery this happens to come in around the 50% mark, which is why that figure is often mentioned. But an AGM has a flatter curve when comparing its discharge on a voltage versus amp-hrs used graph. An AGM battery will run a bit longer, allowing you to use as much as 30% more amp-hrs from the batteries until you get to that 11.8 volts. That really gives you 30% more amp-hrs, which is like getting a free battery on a four battery system.

As to longevity, that will vary according to quality. I suggest getting good batteries, rather than price if you want to go with AGMs. The Lifeline batteries are the best. They will give you the 220 AH that your flooded batteries have (keep in mind that you can only use about 110 AH from your flooded but more like 140 on the AGMs) and are designed to last longer than flooded batteries, although that always depends on the way they are treated.

Your Magnum inverter recognizes the difference between Lifeline and the other brands and will have settings available that let you choose the Lifeline AGM batteries or other AGM batteries as well as flooded batteries. I believe the choices are AGM-1, AGM-2 and Flooded. I don't recall which AGM is for the Concord Lifelines but your Magnum manual will show you.

Can you justify the upcharge for AGMs? That depends. I have eight of them in our coach and generally don't boondock but when I do they give me plenty of power to run the residential fridge and other stuff, especially on a cold night when the Aquahot's diesel burner is running non-stop. I don't have any corrosion issues on my cables either. But eight of them do make a dent on the checkbook. My brother-in-law had two 6 volt batteries in their coach and they needed replacement. He considered AGMs but they are plugged into campsite power 99% of the time (fulltimers) and he didn't have that bad of a corrosion issue. Corrosion comes from outgassing, which comes when the battery is charged with excessive voltage, most notably on the float cycle. If your inverter-charger is doing its job you shouldn't have issues with having to add water all the time or cleaning terminals. So in his case we opted to just buy a pair of flooded batteries.

[buknkat]

Thanks, good thread. I am also in need of replacing my coach batteries (bought coach used, dealer made sure "everything was alright", but somehow neglected to check the water in the flooded coach batteries), so I've been surfing trying to decide which type battery to buy. I think I'm convinced that AGM is the way to go.