AGM battery?
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Topic: AGM battery?
Posted By: OurPodJourneys
Subject: AGM battery?
Date Posted: 22 May 2021 at 12:11pm
Replies:
Posted By: OurPodJourneys
Date Posted: 22 May 2021 at 12:16pm
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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?
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Posted By: offgrid
Date Posted: 22 May 2021 at 2:31pm
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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 |
Posted By: OurPodJourneys
Date Posted: 22 May 2021 at 2:40pm
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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?
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Posted By: podwerkz
Date Posted: 22 May 2021 at 6:11pm
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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! |
Posted By: offgrid
Date Posted: 22 May 2021 at 6:52pm
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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 |
Posted By: offgrid
Date Posted: 22 May 2021 at 7:23pm
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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 |
Posted By: podwerkz
Date Posted: 22 May 2021 at 7:51pm
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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! |
Posted By: offgrid
Date Posted: 23 May 2021 at 5:33am
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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 |
Posted By: campman
Date Posted: 23 May 2021 at 10:44am
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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 |
Posted By: podwerkz
Date Posted: 23 May 2021 at 11:09am
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Glad we could help....yes, differing opinions are bound to happen now and then, it's not arm-twisting, it's just that each person has different experiences and knowledge....some people like Fords, some like Chevys...and oh I've heard of this new upstart named Stellantis....what's that about? Anyway...its time to start an oil thread....analog or digital oil? I mean, dino vs synthetic? No... I'm just kidding, I use plain old 20 weight mineral oil in my r-pod...and I'm happy with that!  ------------- r･pod 171 gone but not forgotten! |
Posted By: OurPodJourneys
Date Posted: 23 May 2021 at 2:25pm
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Thanks for replies to my question, everyone. It's helpful. I've decided to go with traditional lead acid. One reason for considering AGM was the matter of maintenance. But I've learned (the hard way!) what the right things to do are for the lead acid, and will pay more attention to it now. Good travels!
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Posted By: jato
Date Posted: 23 May 2021 at 2:50pm
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Let's muddy the waters a bit further . . . . For about 8 years I have gone back and forth as to 'when' my pair of 12v group size 24 deep cycles die, should I replace them with the same type and voltage or go with a pair of 6v which, being in the golf business, I am quite familiar with. Interesting that for us in the north, the typical life span for a set of 6v golf cart batteries, with exceptional maintenance is 4 years. That is on an older 36 volt system. The same batteries, in the same golf carts, with the same maintenance program in the south will garner 6 years of longevity. For the past 10 years, with Yamaha golf carts leading the way have gone to a 48 volt system using 6 eight volt batteries. Longevity of these in the north is up to 5 years but the caveat of all this is that my basic 12v Interstate batteries are 10 years 5 months and 10 years 2 months old and still work very well for us as we normally boondock without the addition of solar panels or a generator. So . . . . when these decide to 'retire' I may very well replace with another pair of 12 volt batteries. ------------- God's pod '11 model 177 '17 Ford F-150 4WD 3.5 Ecoboost Jim and Diane by beautiful Torch Lake "...and you will know the Truth and the Truth will set you free." |
Posted By: Pod People
Date Posted: 23 May 2021 at 8:21pm
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As I have said many times, our 2 6volt golf cart batteries from Costco have served us well. We boondock a lot and have a lot of discharge/recharge cycles. Those 2 attributes are what makes the golf cart batteries work-ability to discharge/recharge many times and lots of amp hours for boondocking. There is a need for checking the water-but it’s not terrible. I do it on a regular 6 week schedule. I have a small funnel with about 10” of vinyl tubing attached to the end. A gallon of distilled water lasts forever.Pop the cover off, add water if necessary and do the other battery. You don’t have to disconnect any wiring or move the batteries. The Costco batteries cost about $100each. We have had the current ones for over 4years and they are fine. Vann ------------- Vann & Laura 2015 RPod 179 https://postimg.cc/0zwKrfB9"> 
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Posted By: offgrid
Date Posted: 24 May 2021 at 8:25am
Let's see if we can unmuddy this a bit with a little deeper dive into lead acid battery performance. Fair warning, this is probably too nerdy of most folks. There are two distinct impacts of temperature on lead acid batteries which we need to separate here. Both are related to the fact that elevated temperatures increase the rate of chemical reactions. The two chemical reactions to keep track of in PbA batts are internal corrosion rates and charge/discharge reaction rates. First, internal corrosion. You've got lead immersed in sulphuric acid, so corrosion is continuous in any PbA batt. The corrosion rate roughly doubles for every 8-10 degrees C. This corrosion is irreversible and means that the same batteries in hot climates will reach end of life sooner, everything else being equal. Depending on what function the battery is designed for the basic room temperature corrosion rate shelf life can vary from a few years to 20 years of more. But all of them will be have their corrosion life reduced at higher temps. The second chemical reaction is the charge/discharge reaction when the battery cycles. That goes slower when the battery is cold so in effect acts as an internal resistor in series with the battery voltage source. That means that the battery voltage drops faster when the battery is cold, and that effect increases with higher currents. But the capacity is still there, you just need to draw current more slowly or increase the battery temp to get it out. So this effect is reversible. Like with corrosion the impact of temp on capacity is going to depend on the battery design, so this is only true when comparing indentical batteries at different temps. Golf carts batteries are expected to provide a certain minimum amount of current and amp hours regardless of what their temperature is. So if it's cold they start out with less useful capacity to do that and appear to reach end of life sooner. But if you were to warm up those batteries they would must likely still work fine, and do so for longer than batteries which had say in a hot climate since day one. So Jato you might want start a business to collect those well maintained 4 year old batteries in MI and take them to FL where they might get another year or two out if them. For your rpod case, obviously you wouldn't be getting 10 years out if SLI batteries if you were cycling them heavily. But you are clearly very careful in managing discharge in your batteries. So I don't think in your case you should go to deep cycle batteries. They wouldn't last as long because they have a different plate chemistry which allows for deeper and more frequent discharge at the expense of higher internal corrosion rates and self discharge rates. Typically this is done by alloying antimony with the lead in the positive battery plates. For most of us that aren't quite as careful in managing battery discharge deep cycle batteries are more tolerant and can handle more cycled but at the expense if shorter shelf (corrosion) life. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |
Posted By: jato
Date Posted: 24 May 2021 at 7:50pm
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Thanks OG! I was always curious as to why our 12v 'house' batteries on the pod lasts longer than those in the south and then have the exact opposite result when it came to electric golf carts and their batteries. Six years is average for a set of four 12v or six 8 volt batteries. Some even eeek out an extra year but that would be homeowners only. Any 'respectable' golf course with the high greens fees charged would be in trouble if they tried to get an extra year out of their batteries at the expense of having some unhappy golfers who always seem to run out of juice when their cart is way out on the back 9 somewhere. ------------- God's pod '11 model 177 '17 Ford F-150 4WD 3.5 Ecoboost Jim and Diane by beautiful Torch Lake "...and you will know the Truth and the Truth will set you free." |
Posted By: offgrid
Date Posted: 25 May 2021 at 7:59am
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For anyone interested in making a deeper dive into battery wherefores and whatnots check out the Battery University website. Lots (most?) Of what you see on the internet is just someone spouting their baseless opinions but Battery University is well grounded in the science and engineering. Good stuff. ------------- 1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold |