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Old 11-19-2018, 10:57 AM   #1
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AGM battery conversion on 2005 Class A diesel pusher

I’m considering options to replace weak house batteries in our 2005 Winnebago Vectra 40KD motorhome.

My goal is to better equip for occasional dry camping. I would like to minimize genset usage as courtesy to neighboring campers, perhaps 45-90 minutes in morning, and 45-90 minutes early evening. I use a CPAP machine for 7 hours nightly. It would also be nice, but not necessary, to operate home entertainment center (LED TV) for 2-4 hours later in evening.

Here’s what I have to work with:

The battery tray currently has 3 Group size 27 batteries (L/W/H=12.00/6.63/9.06 inches, 90AH each). The battery posts and 4-gauge wires consume most of the space above the batteries, and there is not enough headspace for 11-inch tall golf cart batteries. There is sufficient tray space for 3 Group size 31 batteries (L/W/H=12.90/6.75/9.27 inches, 125AH each).

My OEM Dimensions power station indicates 120VAC current draw of 2 amps with all appliances on propane, LED lights only, everything else powered down. Add another 2 amps for home entertainment center usage. We have 1500W OEM inverter.

I have ResMed 12VDC converter for CPAP machine. My guess is that it uses less than 100 Wh per night.

Deep cycle AGM batteries are appealing, even if they are more expensive. Here’s my imperfect understanding of AGM advantages relative to deep cycle VRLA lead batteries. AGM provides more available energy per unit volume. AGM can be discharged more deeply. AGM charges faster. AGM has longer life span if charger correctly configured. I am considering Vmax 12 Volt 125Ah Group 31 AGM Deep Cycle Heavy Duty Batteries ($280 each) because they consistently have high ratings by off-grid solar users. The OEM Dimension inverter/charger can be reconfigured for safely charging AGM.

We have a 1500KW Onan genset, which has a starter motor connected to house batteries (not chassis batteries). I can start genset with dead house batteries with chassis engine running.

Your comments and recommendations would be greatly appreciated.
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Old 11-19-2018, 11:33 AM   #2
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AGMs don't have more energy the flooded in the same size battery. If they offer more capacity, it may be due to lower cycle life.

AGM can not be discharged any deeper then flooded batteries without shortening their life. They have comparable cycle life's as flooded.

They can be charged at a higher rate but you need the higher rate charger to do that.
You could add a stand alone charger to double up your amp output while dry camping.

Life span is based on cycle life and how you treat them, not chemical makeup. Most lead acid batteries are comparable.

AGMs are practically maintance free and the ones you have researched do have more capacity then some, so there is a gain in capacity with using them. More capacity equals smaller discharges. That equals longer life.

I paid $100 for Sams club GP31s flooded batteries @105 AH. They may not last as long but at less then 1/2 the cost, I'll just replace them sooner.
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Old 11-19-2018, 11:46 AM   #3
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I have 4-Group 31 AGMs in my Winnebago - they came standard from the factory since I have a residential fridge.

AGMs are great because of the maintenance free feature. Other than that, they don't offer a lot more pluses. You still shouldn't use more than 50% of their capacity. They may charge a bit faster because they can take higher voltage. But not much else is different.

I don't want to have to check and add water to my house batteries. They are too difficult to easily reach. So, I wouldn't have anything but AGMs.

Just be realistic about the benefits.
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Old 11-19-2018, 04:49 PM   #4
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If your wallet can handle it up front, lithium is an option. The advantages are numerous, google lithium versus FLA batteries, and there are several good videos listing the pros and cons of each. Over the average life of a LiFeP04 bank, they are competitive price wise to VRLA or FLA batteries. If your charger can be set to put out 14.4V at bulk, they would work for you with your Dimensions (Magnum?) charger. Or, if you're truly interested in some off grid time, add a small (300W-400W) of solar and a charge controller with a lithium setting for batteries, and it will assist/support the OEM charger in keeping them optimized. Battle Born make a 100Ah 12V Group 31 sized battery. I'm looking at a couple (or maybe 3) of them, using similar charging options. They aren't cheap at around US$1000/each, but they'll probably last 10 times longer than an AGM equivalent. Good top end AGM deep cycle batteries aren't cheap either.
Food for thought?
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Old 11-19-2018, 08:45 PM   #5
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If you can get a 12v adapter for your CPAP, you can bypass converting 12v to 120v, and the inescapable losses, then converting it back to 12 or 24 volts for the CPAP. Then you could consider doing what I do, using a dedicated deep cycle battery just to run the CPAP so that it doesn't help run the house batteries down too low.

There's more than one way to skin a cat. I use portable solar panels to recharge my CPAP battery whenever possible, which is always quieter than a generator.
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Old 11-19-2018, 09:40 PM   #6
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Originally we had 4 coach batteries and 2 starting batteries. My solar installer suggested 6 coach/start batteries. I now have 6-6v AGMs in one bank hooked in Series/Parallel. They start the coach and provide the power for living. They provide 670 amps. This system has worked well for nearly 4 years.
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Old 11-23-2018, 10:19 PM   #7
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As said AGMs only benefit is no maintenance, at a high cost. If adding water to batteries is the issue gat a ProFill system, about $120, squeeze a siphon bulb and all batteries are filled in 5 minutes, no caps to remove.

All kinds of AGM battery qualities but they are fussy about charging rates, overcharge and they are gone. Make sure charger is set up properly for them.

As said Lithium’s are the way to go but for techies right now.
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Old 11-24-2018, 06:52 AM   #8
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AGM do have the benefit of being safe to install in non ventilated compartments. Our previous rig we had two in the original space plus two more in the basement for 600 amp-hrs total. For your loads I would want at least 400 AH. We have AGM and wouldn't be without them but the charging requirements are specific. They need to be topped up fully to 100% every week or so to avoid decline, and this takes hours of charging. The best solution IMO is solar, but if you hit a commercial park once a week and top charge them from shore power it works.
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Old 11-24-2018, 04:43 PM   #9
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Quote:
Originally Posted by Harrysait View Post
As said AGMs only benefit is no maintenance, at a high cost. If adding water to batteries is the issue gat a ProFill system, about $120, squeeze a siphon bulb and all batteries are filled in 5 minutes, no caps to remove.

All kinds of AGM battery qualities but they are fussy about charging rates, overcharge and they are gone. Make sure charger is set up properly for them.

As said Lithium’s are the way to go but for techies right now.

I tried one of those auto fill devices once, it turn out to be a Joke.
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Old 11-24-2018, 11:02 PM   #10
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AGM Batteries have more actual capacity.

The AGM’s and GEL sealed cell batteries I am familiar with can be discharged deeper with little or no damage to batteries. The chemistry includes electrolyte limited discharge. They run out of charge when electrolyte is depleted. Flooded cells have excess electrolyte. They run out of charge due to depletion of lead plates. Excess plate depletion causes permanent plate damage.
AGM’s and GEL batteries can be fully discharged with only minimum loss of life. Flooded cells cannot. That effectively gives them more capacity. I used a pair of GELs for over 10 years. They were accidentally discharge fully several times. There was no noticeable loss of capacity 10 years later.
Flooded cell batteries need periodic fast charging to stir the electrolyte otherwise stratification occurs causing plate damage. AGMs and GELs do not since electrolyte is absorbed in glass mats or gelatin like material.
All are subject to deposits of sulfate if stored at low charge levels for long periods. Flooded cells often suffer more due to the excess electrolyte.
All lead acid batteries need venting. Flooded cells vent whenever they are charged. Sealed cells only vent when charge rate exceeds electrolyte’s ability to reabsorb hydrogen and oxygen. Mostly this happens excessively when charging continues after full charge is reached. Venting sealed cells causes permanent damage. More venting means more damage.
Hydrogen vented due to excess charging is flammable and explosive. Venting outside just like flooded cells is the safe way to install them even though they don’t usually vent anything.
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Old 11-27-2018, 05:58 AM   #11
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Over the last week I've spent a lot of time on the battery issue. I needed to replace the 800AH of 4 L16 batteries that sat to long discharged before I bought the rig...batteries only 2 years old and repeated equalizing has not bought them back to life. Yes, a good watering system helps but the corrosion factor makes AGMs worth it for me BUT not at 3-5X the cost.
I found a deal on VLRA batteries...88AH for $70 delivered. BUT, the more I researched VLRA and the lower voltage they need to be charged at...not with your engine alternator...to high a voltage, I passed on them even though they probably have a better cycle life than AGMs.

I did find a deal on AGMs in Atlanta but instead of the Interstate (probably 5 years old) I bought 11 of their Odyssey 1600amp AGMs. All tested at 1600 amps +/- 10 amps although several did not so sat them aside. By bringing 11 cores the price was $75 each plus sales tax. 12 would fit perfectly where I now have 4 L16, but 11 gives me room to tie all the cables together.

Instead of 800AH this will give me 1,375AH and while these are not FRESH batteries ($500+ for a recently built one) the 170% extra capacity will let me decrease the amount I draw them down, increasing the # of cycles and hopefully, the years I can get out of them. $890 instead of 11 X $500 = $5,500+...not a hard decision and worth the 100 miles to buy them.

Interstate https://atlanta.craigslist.org/atl/p...749551305.html
Odyssey https://atlanta.craigslist.org/sat/e...736232796.html
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Old 11-27-2018, 07:11 AM   #12
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Quote:
Originally Posted by Ivylog View Post
Over the last week I've spent a lot of time on the battery issue. I needed to replace the 800AH of 4 L16 batteries that sat to long discharged before I bought the rig...batteries only 2 years old and repeated equalizing has not bought them back to life. Yes, a good watering system helps but the corrosion factor makes AGMs worth it for me BUT not at 3-5X the cost.
I found a deal on VLRA batteries...88AH for $70 delivered. BUT, the more I researched VLRA and the lower voltage they need to be charged at...not with your engine alternator...to high a voltage, I passed on them even though they probably have a better cycle life than AGMs.

I did find a deal on AGMs in Atlanta but instead of the Interstate (probably 5 years old) I bought 11 of their Odyssey 1600amp AGMs. All tested at 1600 amps +/- 10 amps although several did not so sat them aside. By bringing 11 cores the price was $75 each plus sales tax. 12 would fit perfectly where I now have 4 L16, but 11 gives me room to tie all the cables together.

Instead of 800AH this will give me 1,375AH and while these are not FRESH batteries ($500+ for a recently built one) the 170% extra capacity will let me decrease the amount I draw them down, increasing the # of cycles and hopefully, the years I can get out of them. $890 instead of 11 X $500 = $5,500+...not a hard decision and worth the 100 miles to buy them.

Interstate https://atlanta.craigslist.org/atl/p...749551305.html
Odyssey https://atlanta.craigslist.org/sat/e...736232796.html
Hope it works out for you.

AGM batteries are VRLA. Valve Regulated Lead Acid.

Both AGM and Gell are different composition VRLA batteries.


Here is a manual for the batteries. They seem to need a pretty high charging amperage.US-ODY-TM-002_1214.pdf
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Old 11-27-2018, 07:21 AM   #13
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You can get AGM GCs for about 2X the $ of FLA.
It's still a personal decision whether the convenience is worth the extra $. IMO there is little real justification other than convenience.
Don't get me wrong I have 4 AGM in my boat and will consider them for MH house when the time comes. I won't rationalize the $ on anything other than convenience... and maybe the $ of a pair or two of jeans w acid holes... wait a lot of people pay extra for that????
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Old 11-27-2018, 01:28 PM   #14
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AFAIK,
AGMs are better in cold environments, whether deployed or stored. They resist freezing better than gel or flooded.
Their rate of self discharge is probably the lowest of all of the more common lead acid choices, so they store longer with less harm when not in use.
Since the electrolyte is embedded in the glass mats between the plates they are virtually spill proof, and can be used in physical orientations other than sitting upright.
They can usually handle repeated deeper discharge rates than their flooded peers.
They can accept charge at a faster rate than the other common options, so recover from deep discharges more quickly.
They are physically maintenance free. Most hydrogen gas is reabsorbed in the mat inside the battery awaiting recharge.
They are more convenient, for most of the prior points.
Yes, they are typically more expensive, but I don't think convenience is the only advantage over most of the other gel or flooded options.
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