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Joined: 01 May 2016
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Topic: AGM battery?
Posted: 22 May 2021 at 12:11pm

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Posted: 22 May 2021 at 12:16pm

Sorry, that 1st post was mine, sent without a message.

My question: I use two 12V lead acid batteries for 2016 179. They need to be replaced. We do a fair amount of boondocking. Am thinking of switching to AGM. Are any modifications needed, or do I simply switch the batteries? Are there important pros and cons to AGM I should consider before committing to AGM?

offgrid

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Posted: 22 May 2021 at 2:31pm

Pros: no maintenance

Cons: no way to add water so they are sensitive to overcharging

Expensive

Hard to get in 6v configuration, so the batteries have to be connected in parallel, which is not ideal because they don't get equal charging and discharging when in parallel.

I'd recommend 2 6v GC2 size golf cart batteries in series. But you have to be willing to check and add distilled water at regular intervals. If not, go for your AGM's.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

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Posted: 22 May 2021 at 2:40pm

Thanks. That's helpful.

Two questions: why use 6V instead of 12V?

And ... I keep reading cautions about not overcharging AGM. But how does one avoid overcharging?

podwerkz

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Joined: 11 Mar 2019
Location: Texas
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Posts: 966

Posted: 22 May 2021 at 6:11pm

The only way to always avoid overcharging AGMs is to chronically undercharge them. Nature of the beast, but if the level of constant under-charge is in the 80 to 95% range, then you are good to go.

But, in this application (tongue mounted battery on a travel trailer) where the batteries are outside (no interior venting concerns) exposed to temperature extremes, but wont be turned sideways in any normal use (AGM are generally spillproof) and the water refill ports are reasonably accessible, flooded batteries really are the most bang for the buck, very robust, easily replaceable, and almost 100% reliable, usually made in the good ol USA.

I take a different fork in the road when it comes to 6v batteries than offgrid...I recommend and use 2 12v batteries in parallel and it works fine. If one cell in one battery shorts or opens, you can still use the remaining battery for some time if needed... And if your tow vehicle battery dies in the middle of nowhere, you can drop in your RV deep cycle (assuming it has starter posts) and continue on your merry way. Virtually all class 8 OTR semi truck tractors use 4, 12v batteries in parallel. It's proven, it works, and the replacements are reasonably priced and available just about everywhere you are likely to be.

But with a pair of 6v GC batteries, if a cell shorts or opens in one battery, you are 'dead in the water'...so to speak. I know, I tried it with an old motorhome I had. Not gonna do that again.

At any rate, your choice...pros and cons for each solution.

r･pod 171 gone but not forgotten!

offgrid

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Joined: 23 Jul 2018
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Posted: 22 May 2021 at 6:52pm

I'll give you 3 answers to the first question.

1) Batteries aren't identical, and as they age they tend to vary more. Specifically, each one will have a different internal series resistance. If they are in series that won't matter but if they're in parallel the one with lower series resistance will take (and provide) more current and so will get more cycling over time.

2) Two 6v batteries have a total of 6 cells. Two 12v batteries have 12 cells. So for the same amphour capacity the 6v configuration will have half the cells with twice as much lead and acid in each. The battery plates will be thicker and more robust.

3) This one is specific to our use case. 6v golf cart batteries are very common in this size so available from many manufacturers at good prices. Also, two GC2 size golf cart batteries are the largest that will fit in the rpod rack so give you the most capacity.

Re how to be sure that you don't overcharge AGM batteries? Use a good quality charger with a setting for AGM's, which will be slightly lower in voltage for each charging stage than for a flooded battery. Will the WFCO charger in your rpod do the job? Debatable.

All this bring said, if you don't feel you will remember to check the water level in flooded batteries they by all means get AGM's. If you do get 12v AGM's then take the positive output lead from one and the negative output from the other, that will keep the wire resistance the same for both.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

offgrid

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Posted: 22 May 2021 at 7:23pm

If a cell in one of two parallel batteries shorts you will get circulating currents as the good battery dumps it's charge into the battery with the bad cell trying unsuccessfully to charge it. The current can get really high. Ask me how I know.

You also have twice as many cells to fail with the parallel 12v configuration.

Large trucks use parallel batteries because they need high starting currents. It's a SLI (starting, lights, ignition) not a deep cycle apucation like the rpod is. Ok. Skip the "I" part for diesels...

Off grid solar is a deep cycle application, and standard practice is to avoid paralleling batteries when possible. Of course, it's not always possible in large battery systems, so battery paralleling is done when needed.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

podwerkz

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Joined: 11 Mar 2019
Location: Texas
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Posted: 22 May 2021 at 7:51pm

Well except for the fact that overnights in a truck with the engine off, with the four 'starting' batteries, we often run what are called, 'hotel loads' in transportation lingo...meaning, TV, stereo, 12v heated mattress pads, laptop, LED lights, phone charger, cell phone booster, OBC unit (satellite comm terminal) webasto bunk heaters, sometimes gameboys, coffee makers, lunchbox heaters, microwave ovens, computer printers, interior air circulation fans, etc etc etc....

Trust me, the 4 truck batteries are not JUST for SLI. There is a person living in that thing 24/7 most of the time, and he or she needs the power to operate electrical items whether the main engine or the APU is running or not.

Again, not arguing, but there is a long successful history of using 12v batteries in parallel no matter what a few RV people recommend should not be done.

r･pod 171 gone but not forgotten!

offgrid

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Joined: 23 Jul 2018
Online Status: Offline
Posts: 5290

Posted: 23 May 2021 at 5:33am

We need to separate the discussion of 12v vs 6v from the discussion of deep cycle vs. SLI vs dual use "marine" batteries. SLI batteries have to provide very high currents to the starter for short periods. So high current, low amp hours. Deep cycle batteries provide much lower currents to house loads for much longer periods, so low current, high amp hours. So called "marine" or dual use batteries are a compromise between the two, because on boats batteries Have to both start the engines and run the house loads.

Battery engineers have been improving and optimizing their designs for generations. That's why lead acid batteries are still very much with us even though the technology has been around since Gastone Plante invented it in 1860. Deep cycle and SLI batteries are differently. Different chemistry, different plate construction and thickness. Any of them could be made at any voltage, at least in theory. In practice the design features that make for a good deep cycle battery (thick, heavy plates with lots of lead and lots of electrolyte) make them dang heavy at 12v.

The point is to use the proper type of battery for the application. RV house loads are low current long duration so the kind of use profile deep cycle batteries are designed for. Golf carts and solar applications are similar. That doesn't mean you can't use an SLI battery to run your rpod house loads or a deep cycle battery to start and engine, they just won't work as well. Use the right tool for the job at hand.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

campman

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Joined: 26 Mar 2021
Location: La Salle, MB
Online Status: Offline
Posts: 209

Posted: 23 May 2021 at 10:44am

This threads discussion on batteries and the various types is one of the reasons this forum is such a great go-to reference (and should be an easily accessible must-read for anyone else mulling over their battery choices!). I would suggest most people aren't aware of how important this decision is and may end up with the wrong battery(s).

My wife and I were just discussing this again this am as I try to drill down and find the right purchase for us. I had leaned towards 6v AGM as that is what we have in our offgrid cottage. I like AGM as they don't off-gas explosive/corrosive/poisonous gasses (our 8 large solar AGM's are inside our cottage so we can warm them up in the extreme cold of our winters before we use them).

Trailer needs are different so now leaning towards GC x2 normal lead acid batteries.

Offgrids points have cemented my thoughts as to what our needs are and I am easily capable of maintaining them where they will sit, on our trailer A frame.

The cost comparison is very important and bang for the buck matters...battery performance for what it is designed to do very important as well and the capability of the battery is something to keep in mind as well.

We have decided to stay away from the LiFePo battery and the required investment in the needed specialty items to make this expensive upgrade a reality. I know it will be revisited, but for now we aren't ready to make the plunge. One step at a time, eh?

So glad OurPodJourneys has posted this very interesting question regarding "to AGM or not to AGM"!

Andy

Andy and Laurie
'16 F150 5.0 4X4 w/factory tow pkg
'21 RP192
"If the women don't find you handsome...at least let them find you handy!"
Red-Green

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OurPodJourneys Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 01 May 2016 Online Status: Offline Posts: 8	Topic: AGM battery? Posted: 22 May 2021 at 12:11pm


OurPodJourneys Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 01 May 2016 Online Status: Offline Posts: 8	Posted: 22 May 2021 at 12:16pm
	Sorry, that 1st post was mine, sent without a message. My question: I use two 12V lead acid batteries for 2016 179. They need to be replaced. We do a fair amount of boondocking. Am thinking of switching to AGM. Are any modifications needed, or do I simply switch the batteries? Are there important pros and cons to AGM I should consider before committing to AGM?

offgrid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290	Posted: 22 May 2021 at 2:31pm
	Pros: no maintenance Cons: no way to add water so they are sensitive to overcharging Expensive Hard to get in 6v configuration, so the batteries have to be connected in parallel, which is not ideal because they don't get equal charging and discharging when in parallel. I'd recommend 2 6v GC2 size golf cart batteries in series. But you have to be willing to check and add distilled water at regular intervals. If not, go for your AGM's.
	1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold

OurPodJourneys Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 01 May 2016 Online Status: Offline Posts: 8	Posted: 22 May 2021 at 2:40pm
	Thanks. That's helpful. Two questions: why use 6V instead of 12V? And ... I keep reading cautions about not overcharging AGM. But how does one avoid overcharging?

podwerkz Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 11 Mar 2019 Location: Texas Online Status: Offline Posts: 966	Posted: 22 May 2021 at 6:11pm
	The only way to always avoid overcharging AGMs is to chronically undercharge them. Nature of the beast, but if the level of constant under-charge is in the 80 to 95% range, then you are good to go. But, in this application (tongue mounted battery on a travel trailer) where the batteries are outside (no interior venting concerns) exposed to temperature extremes, but wont be turned sideways in any normal use (AGM are generally spillproof) and the water refill ports are reasonably accessible, flooded batteries really are the most bang for the buck, very robust, easily replaceable, and almost 100% reliable, usually made in the good ol USA. I take a different fork in the road when it comes to 6v batteries than offgrid...I recommend and use 2 12v batteries in parallel and it works fine. If one cell in one battery shorts or opens, you can still use the remaining battery for some time if needed... And if your tow vehicle battery dies in the middle of nowhere, you can drop in your RV deep cycle (assuming it has starter posts) and continue on your merry way. Virtually all class 8 OTR semi truck tractors use 4, 12v batteries in parallel. It's proven, it works, and the replacements are reasonably priced and available just about everywhere you are likely to be. But with a pair of 6v GC batteries, if a cell shorts or opens in one battery, you are 'dead in the water'...so to speak. I know, I tried it with an old motorhome I had. Not gonna do that again. At any rate, your choice...pros and cons for each solution.
	r･pod 171 gone but not forgotten!

offgrid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290	Posted: 22 May 2021 at 6:52pm
	I'll give you 3 answers to the first question. 1) Batteries aren't identical, and as they age they tend to vary more. Specifically, each one will have a different internal series resistance. If they are in series that won't matter but if they're in parallel the one with lower series resistance will take (and provide) more current and so will get more cycling over time. 2) Two 6v batteries have a total of 6 cells. Two 12v batteries have 12 cells. So for the same amphour capacity the 6v configuration will have half the cells with twice as much lead and acid in each. The battery plates will be thicker and more robust. 3) This one is specific to our use case. 6v golf cart batteries are very common in this size so available from many manufacturers at good prices. Also, two GC2 size golf cart batteries are the largest that will fit in the rpod rack so give you the most capacity. Re how to be sure that you don't overcharge AGM batteries? Use a good quality charger with a setting for AGM's, which will be slightly lower in voltage for each charging stage than for a flooded battery. Will the WFCO charger in your rpod do the job? Debatable. All this bring said, if you don't feel you will remember to check the water level in flooded batteries they by all means get AGM's. If you do get 12v AGM's then take the positive output lead from one and the negative output from the other, that will keep the wire resistance the same for both.
	1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold

offgrid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290	Posted: 22 May 2021 at 7:23pm
	If a cell in one of two parallel batteries shorts you will get circulating currents as the good battery dumps it's charge into the battery with the bad cell trying unsuccessfully to charge it. The current can get really high. Ask me how I know. You also have twice as many cells to fail with the parallel 12v configuration. Large trucks use parallel batteries because they need high starting currents. It's a SLI (starting, lights, ignition) not a deep cycle apucation like the rpod is. Ok. Skip the "I" part for diesels... Off grid solar is a deep cycle application, and standard practice is to avoid paralleling batteries when possible. Of course, it's not always possible in large battery systems, so battery paralleling is done when needed.
	1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold

podwerkz Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 11 Mar 2019 Location: Texas Online Status: Offline Posts: 966	Posted: 22 May 2021 at 7:51pm
	Well except for the fact that overnights in a truck with the engine off, with the four 'starting' batteries, we often run what are called, 'hotel loads' in transportation lingo...meaning, TV, stereo, 12v heated mattress pads, laptop, LED lights, phone charger, cell phone booster, OBC unit (satellite comm terminal) webasto bunk heaters, sometimes gameboys, coffee makers, lunchbox heaters, microwave ovens, computer printers, interior air circulation fans, etc etc etc.... Trust me, the 4 truck batteries are not JUST for SLI. There is a person living in that thing 24/7 most of the time, and he or she needs the power to operate electrical items whether the main engine or the APU is running or not. Again, not arguing, but there is a long successful history of using 12v batteries in parallel no matter what a few RV people recommend should not be done.
	r･pod 171 gone but not forgotten!

offgrid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290	Posted: 23 May 2021 at 5:33am
	We need to separate the discussion of 12v vs 6v from the discussion of deep cycle vs. SLI vs dual use "marine" batteries. SLI batteries have to provide very high currents to the starter for short periods. So high current, low amp hours. Deep cycle batteries provide much lower currents to house loads for much longer periods, so low current, high amp hours. So called "marine" or dual use batteries are a compromise between the two, because on boats batteries Have to both start the engines and run the house loads. Battery engineers have been improving and optimizing their designs for generations. That's why lead acid batteries are still very much with us even though the technology has been around since Gastone Plante invented it in 1860. Deep cycle and SLI batteries are differently. Different chemistry, different plate construction and thickness. Any of them could be made at any voltage, at least in theory. In practice the design features that make for a good deep cycle battery (thick, heavy plates with lots of lead and lots of electrolyte) make them dang heavy at 12v. The point is to use the proper type of battery for the application. RV house loads are low current long duration so the kind of use profile deep cycle batteries are designed for. Golf carts and solar applications are similar. That doesn't mean you can't use an SLI battery to run your rpod house loads or a deep cycle battery to start and engine, they just won't work as well. Use the right tool for the job at hand.
	1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold

campman Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 26 Mar 2021 Location: La Salle, MB Online Status: Offline Posts: 209	Posted: 23 May 2021 at 10:44am
	This threads discussion on batteries and the various types is one of the reasons this forum is such a great go-to reference (and should be an easily accessible must-read for anyone else mulling over their battery choices!). I would suggest most people aren't aware of how important this decision is and may end up with the wrong battery(s). My wife and I were just discussing this again this am as I try to drill down and find the right purchase for us. I had leaned towards 6v AGM as that is what we have in our offgrid cottage. I like AGM as they don't off-gas explosive/corrosive/poisonous gasses (our 8 large solar AGM's are inside our cottage so we can warm them up in the extreme cold of our winters before we use them). Trailer needs are different so now leaning towards GC x2 normal lead acid batteries. Offgrids points have cemented my thoughts as to what our needs are and I am easily capable of maintaining them where they will sit, on our trailer A frame. The cost comparison is very important and bang for the buck matters...battery performance for what it is designed to do very important as well and the capability of the battery is something to keep in mind as well. We have decided to stay away from the LiFePo battery and the required investment in the needed specialty items to make this expensive upgrade a reality. I know it will be revisited, but for now we aren't ready to make the plunge. One step at a time, eh? So glad OurPodJourneys has posted this very interesting question regarding "to AGM or not to AGM"! Andy
	Andy and Laurie '16 F150 5.0 4X4 w/factory tow pkg '21 RP192 "If the women don't find you handsome...at least let them find you handy!" Red-Green