Battery Desulfation Demonstration Start to Finish - Part 2/2 

Thanks for the support! This channel is not very active at the moment so videos are currently posted infrequently. Perhaps in the future that may change.

keep them outside give it plenty of sunlight, rain and throw some salt on the terminals every now and then :)

Yes specifically deep cycle battery's that seldom get cycled

@@LewisMoten 7 Months Ago!!!🤣

You're a weird person. I like you.

These videos make me want to learn more about the equipment and what you can do with it. Besides i am tired of buying farm machines batteries they die and freeze over the winter great ohio weather

@@Dm65-gpyThe best thing is to take the batteries out and store them where they won't freeze and charge them every once in a while. Otherwise a previously frozen battery will usually recover to some extent if you desulfate it. I've done this many times and they usually give many years of service after even though their reliability will always be in question: It may last 10 years or it may last 1 month. Freezing a battery isn't good.

@@knurlgnar24 it such a pain to take them all but i do need to I agree. I think im going to order a power supply should i get a 30v 5 amp or 60v 5amp they also have some 10amp

Any thoughts on this? Thanks

Nice work! Most of the time this sort of thing isn't really economical but on occasion it can be. There are businesses that specialize in recovering and reselling forklift batteries for example.

@@knurlgnar24 Yup. It was a good exercise. Later my neighbour put his old car battery on the side walk, a big ass one for a large Mercedes Diesel. I scaled up the charging and discharging with my huge lab supply (up to 20A) and a massive electronic load form my employer. I used jump starting cables to connect the battery to the load. They got hot. In fact, I was lucky to play it safe and be physically present and monitoring, because one of the terminals' isolation caught on fire (due to the high temp cause by the contact resistance) while testing at 80A(!). Unfortunately, that battery had a defective cell as well and after charging and sitting for 24hrs the clamp voltage dropped to below 12V by itself. I did get some cash out of it when recycling though, as it was very heavy!

Yes, the wire color convention for DC is not consistent. Is Black hot or is Black neg/gnd? What is white? Black is ground/neg on battery systems so white must be positive/hot? No, wait, white is neutral. No? ???

@@knurlgnar24 - For our rings here in the U.K. we use brown = live, blue = neutral and green/yellow stripes for earth.. We used red = live, black = neutral (earth y/g) until a few years ago. That could lead to an interesting situation for a Brit emigrating to N.A. who decides to do any electrical work!

It's a lot more straight forward in Europe. Single-phase 230V, 3 phase 400V, unique colours, you guys are nuts. I'm over here; www.fieldlines.com/index.php/topic,150161.0.html I do pretty similar work to yourself. Kind regards, Liam.

If the batteries are full charged but reading low on your hydrometer then they are likely sulfated. Depending on the battery cell size and type you may need something more like a 10A supply and they may vent a lot during desulfation, so be ready for that and make sure they don't run low on electrolyte. There are safety concerns working with large flooded batteries but a lab supply of sufficient amperage will work on them just the same as a smaller battery. Assuming you have a lead-antimony battery bank a 5A supply probably isn't enough for a forklift battery/cell.

@@knurlgnar24 Hi, Thank you for fast reply. I was not expecting such a rapid responce. Yes, that hydrometer reading was after charging batteries. I have forklift battery charger which should be original. there are lights, which indicate cell charge from 2.1 to 2.65. While charging reading was highest at 2.52. immediatly after charging 2.3 and it is dropping slowly to 2.08 ( few days after charge) I´m keeping eye on eletrolyte levels and I also have fume extractor available. Do you have safety concerns beyond hydrogen build up? Those seems to be 500 Ah cells so most likely lab power supply is not right one for the job. Since all 12 cells are quite same condition maybe I can recondition battery with original charger? Just enough charge and drain -cycles? Thank you alredy in andvance for any help you can provide.

That's a good guess on the capacitors. I suspect if those batteries were new and never used they would have come back. No guarantees though!

I think what he meant, was that with the cutoff voltage set at 9.5v it would actually be stopping at 10.5v.

Excellent video series by the way. Very informative. I've learnt a lot!

I was discharging it at the C/1 rate, and at that discharge rate the datasheet claimed the battery had about 3.5Ah. I would have gotten different results if I used a more appropriate C/10 discharge rate but I didn't want to wait a day per cycle.

@@knurlgnar24 Thanks - see, told you I'm learning a lot!

Yup. Didn't realize the large voltage drop until the test was started and as described in the video it doesn't really matter anyway.

Yes, this exact same method will work on a 6 volt battery. A power supply like this would be sufficient for a 100Ah battery and I have used them on my bank of 100Ah 12V batteries.

The datasheet for the battery shows discharge curves for various discharge rates. At the rate I was discharging the battery 2.6Ah was about 75% of rated capacity. You can only get the nameplate 7.2Ah if the battery is discharged very slowly.

@@knurlgnar24 I understand. Thanks for taking the time to reply.

If the battery sat uncharged over the summer it can be saved almost for certain. AGM does not require more voltage than flooded batteries - the voltage required is related to the chemistry which is generally grouped into three loose categories: Pure lead, lead calcium, and lead antimony. I don't know your battery but it is likely lead calcium which is the same chemistry as nearly all flooded car SLI batteries today in the USA. It depends on how much time you have but around 14.6 to 14.8V is a good voltage for these as you stated. I'd actually suggest 15V for a flooded battery as the water can be replaced. I don't know your exact situation but I'm thinking 14.5V would be a good start point with 12hr 14.5V desulfation durations after full charge each cycle to avoid too much water loss. Each discharge cycle would then involve charging normally followed by another 12hr 14.5V desulfation. If your battery takes little to no current you can safely start at as high a voltage as you want and limit the current to an amp or two to get the process started until you get that 1st charge done. When cycling if the battery is stubborn you may need more than 14.5V, but much above 15V and you're likely to lose a good amount of water and shorten battery life. It depends a bit on your patience and available time commitment. There's nothing wrong with leaving it on a charger for weeks at a time at something in the low 14V range too. That's a completely acceptable method if you have the time.

@@knurlgnar24 Thx. It's very nice you answer so quickly. Cheers!

Main reason for trying to determine this, is to get a more accurate Ah reading after each discharge cycle. If discharge is started at a different voltage and/or charge capacity level, then tests aren't apples-for-apples.

You unfortunately won't know when it is fully charged while desulfating. This is one of the reasons the battery must be cycled to test its performance. You don't want to force-overcharge it longer than necessary and cycling will tell you whether it is still improving or not.

That depends on the overall condition of the battery. If a battery was neglected and just sat unused then you will have a long service life after desulfation in most cases. If it was in use and got positive plate corrosion, buckling plates, water loss, etc then your results won't be as good.

@@knurlgnar24 interesting! so it depends on WHY it became sulfated in the first place. btw you mentioned the idea of doing a video on how to PROPERLY maintain/store a battery. i'd love to see a video about that and why a float charger isnt enough etc

Yes, but gel batteries will require a low current limit to avoid creating voids in the electrolyte. I am not sure exactly what the current level needs to be for any particular battery.

Are all of the cells filled with a proper amount of water? If you open the inspection caps (assuming this battery has them) what condition do the plates appear to be in? If they are warped or the electrolyte cloudy/opaque the battery has issues other than straight sulfation. If you got the battery with 11V then it likely does NOT have a cell short. That's good. It may still be past it's useful life and simply need to be recycled though. 1. If one cell gets warmer than the rest and the electrolyte level is proper then this cell has a higher voltage drop when charging than the others. This could be for a variety of reasons including less active material due to excessive plate shedding, contaminated or incorrect pH acid, sulfation, a cell short, etc 2. I believe the current is going up simply because the battery is entering 'thermal runaway' during the charge cycle. This is normal. To prevent it voltage/current needs to be reduced. 3. As for balancing cells this would best be done by accessing individual cells, but this video covers the more practical approach of only accessing the 12V terminals. To balance you overcharge, cycle, overcharge, cycle a few times. Then they should be balanced. If the battery is 12.8V after charging and sitting for a few days have you measured its capacity or discharge rate ability? Sounds like it may be recovered? If not I suspect it has issues other than sulfation and needs to be recycled. Batteries have a finite lifespan and there's nothing that can be done to overcome that. Plate corrosion and active material shedding eventually kill all lead acid batteries. Even the desulfation process causes shedding which is irreversible.

Also, hello to you in Germany from the United States! Your battery is likely a Lead Selenium alloy which does not commonly exist in the USA and I have not worked with that particular chemistry before. As I understand it is functionally a cross between our common Lead Calcium batteries (used in cars) and Lead Antimony batteries (used in forklifts and the like). Your battery likely outgasses more than the lead calcium battery shown in this video which may explain your higher leakage current during charging. I wouldn't worry about the slightly lower finishing voltage or .8A charge voltage for this reason on your battery.

@knurlgnar24 Hi Knurlgnar. Greetings again from Germany. Thanks for your help!!!!! I looked in the internet for my MB A0055411001 VRLA battery, but didn't find the original technical data from 2008. Now I understand that VRLA is some kind of gel battery but the new ones are all Varta/MB AGM G14 batteries. What is the difference between VRLA and AGM? To me it seems very similar. The battery case on the new ones is silver but mine is black. Sealed with some strange looking caps over the chambers, that don't have a possibility to open them (one way seal) without demaging the caps, to add water. The new ones are completely sealed. On the top it says "VRLA-BATTERY DON'T OPEN". When I charge the battery, I cannot hear anything bubbling, except I charge it with current for 7 cells for some time with 5A. Then it starts to bubble minimally. At 2A not at all. That's how I got it back to life. Since then it takes charge with 12V (14,7V at 1,225 rate) normally. About the battery: It was build in a C-class limousine with all the gimmicks that are there, like auto light +++ and was used mostly in town. The neighbor's son then forgot to turn something off over night and then it was almost dead at 11V. After I got the battery, I directly charged it and the voltage came back up, but not the capacity to start a car. That's when I started circling it with a 500W Inverter but it still didn't got enough capacity to start my old 1,9 VW Tdi PD. Then I tried overcharging it with current for 7 cells (14V max 17,15V at 1,225 rate) with 5A over short time or 1A or 2A over few hours until it broke loose and started charging better with 12V. The voltage dropped just like in your first video down to normal voltage even if I charge it with 14V from time to time over short periods of time. The voltage settles at about 12,7-12,8V when I lett it cool down. After charging it like this the capacity came back, even if not completely. Now it can start my diesel without problems, but I want to complete the task before using it there instead of my current 70A battery that collapsed on me last week. I guess my engine with 477K kilometers is possibly not charging the battery enough. I must check that. I've read somewhere that the thermal run that you described is not good, so now I charge the battery with less current at the end. Over night with 1,2A and 12V the charge voltage was 14,14V. I guess that is better. About the warm cell and balancing, I will continue to charge and discharge the battery as you told me until the cells are doing better and are well balanced. Only then will I use it in my car. A little question at the end: Do you thing that I should get a stronger Inverter then 500W to drain the battery faster, quasi as if it is under heavy load to simulate the starting of the engine or should I stay at 500W? Anyways, Thank you very much for helping me out, Knurlgnar. I'll report the results when I'm done. Be blessed!

@@jazzbuzz7866 I wouldn't be concerned about the load you are using to discharge the battery. The only important factor is that the battery is being cycled. It sounds to me that you are doing everything right from the perspective of someone who is attempting to recover a battery without disassembling or replacing the electrolyte which is beyond what my experience covers, and is beyond what I believe is practical for most individuals. If someone has $20k of batteries then it may be worth it but not for people like you or me. If cycling and overcharging the battery doesn't bring it back up to a useful status for your application then I don't think I have much more to offer you. That battery either is good enough for your purpose or it has reached the end of its useful life.

@@knurlgnar24 Okay Knulgnar. Thanks for your answer. It is not so much the money, but checking out how the recovery is done and enjoying the process of bringing the battery back to life is very satisfying. Somehow I like using things until they are completely scrap and then get rid of them. I just like the challenge. Here in Germany the people just throw everything away as soon that it doesn't work 100‰ and I cannot stand that. Maybe my makedonian roots interfere, becouse in MK if something can be repaired, we repair it and do not throw it away. Besides, as a man I love such technical challenges. I also try with my son to repair all of our old cars, even if we're not car mechanics. Again thanks for everything and see you on the Chanel. I'm right now checking your Inverter-videos. Bye

"unequivocally", no, but for practical purposes one does not need an electronic load that can do the highest discharge rate desired to get good data. For a useful IR measurement you'll likely want to discharge using an inverter or something of the like, as AC IR testers do not give measurements that can be plugged into an equation that results in an accurate discharge curve for loads higher than what was directly measured. I would instead argue that no electronic load is needed and that it instead only makes the process easier. The best method is to discharge at the correct test load and this can be done with an inexpensive power inverter. It's just a bit of a pain in the *ss.

@@knurlgnar24 yes I know this inverter trick of yours and You greatly presented it in the first part of this video but as you admitted an electronic load is simply more convenient. Speaking of which, I guess your answer would essentially be that one should discharge battery at its max. load power to make a reliable test of the battery in its application environment, so for medium-to-high power batteries the 350W Rigol is not the way to go. Is that your answer? (or discharge at a typical load power, which in my example of a 500W vehicle engine means simply max. load power anyway)

​@@knurlgnar24 BTW, I so insist on this discharge power because although I know little about batteries I think that even after "successful" reconditioning, a battery's internal resistance might be so high that it will give a fraction of nominal power. For example a battery like that in this video may give above 12V alright (or a perfect nominal open-circuit voltage), but the current flow out of it will max out at half of the nominal one, say instead of 12A, 6A at the most. Is this basically correct what I am saying or does the internal resistance of a battery not work like that? (as far as I remember a battery may be represented simply as a serious of a voltage source and a resistor, the only difference being that this "resistor" changes its resistance - but how and to what extent I do not know)

I showed the graph from the manufacturer showing Ah rating vs discharge rate. 7.2Ah was probably at the 20hr rate and I was discharging at a much higher rate which results in lower measured capacity.

@@knurlgnar24 Thanks for a quick reply.

@@knurlgnar24 As far as I understand you can safely get 1/2 the rated capacity out of the battery. If you take out more than that you are doing damage to the battery. That's why IMO.

These batteries are rated at 7.2Ah, not 2.7Ah. This is the C/20 capacity, at 7.2Ah you'd expect it to measure half the capacity.

@@eDoc2020 my fault

If the battery was used and never sulfated then I concur with your experience. Batteries that have failed due to undercharging or poor maintenance are a good candidate for this recovery. I suspect you haven't mistreated your batteries and as a result the methods in this video aren't applicable to your application/experience.

@@knurlgnar24 it is actually painful for me to see all that equip and time.....well; but, now, ANY TIME you see that DEATH NUMBER, buy a new battery please: . . . well,the death number is 10.7 or 10.8 or.... you now know what that means; it's DEATH (of one cell, AND of the non replaceable 6 cell rippoff arrangement they sell us).

Thats' to EZ. I did collage gud. www.youtube.co/watch?v=wv4eTE0aUiQ Next time Gadget. Next time.

Ullllu

And that's exactly the kind of excitement I deliver!

If it's not in the DSM-5 it should be, I share your condition. My condolences..

@@knurlgnar24 I thought this was the support group for that?

Hi Fred! Based on what I discovered in this video and where I salvaged it from I suspect this battery was never installed and instead was stored for a long period of time and 'failed' self test immediately upon installation and was then scrapped. Usually used UPS batteries are only useful for scrap.

@corey Babcock I think his batteries were in service for several years before he saved them from the scrap heap and that was over 5 years ago and many of them are still at 100% capacity. He made some interesting videos on them.

@corey Babcock I was amazed to find, when I had to replace my car's battery, that the one in it was the original one from the faactory. It's date marking showed that it was 11 years old !

I know this is an old comment but I still use these same batteries at least once per year as a test to demonstrate how they will perform powering my household needs with generator backup. No issues so far.

Thanks a lot for this video. I am currently trying to salvage two similar batteries that has been totally discharged. I am a bit at loss about when to stop the high voltage "overcharging". The thing to watch out for, you say, is temperature. How high temperature is "ok"?

I wouldn't consider 'controlled overcharging' to be a technical term as it is more a description of the process. A sulfated battery when charged according to standard charging procedures as documented by the battery manufacturer will stop accepting charge well before it is truly charged. The sulfation isn't going to be converted back into useful active material in any substantial portion unless forced to by charging more aggressively than normal use procedures. Even equalization procedures don't really reverse sulfation to a significant extent in most cases as it is too tame to do much. What is needed is an overcharge condition that goes beyond ordinary use procedures. An overcharge severe enough to permanently damage the battery is required and this must be controlled by the user for obvious reasons. Fortunately the easiest part of a sulfated battery to damage is the sulfation and so it can improve the battery performance at the expense of some irreversible corrosion and shedding of active material of the battery plates, something that would otherwise be highly undesirable in a battery that is in good condition.

@@knurlgnar24 Thank you for the reply, i understand now what you meant/mean by that term. But still unclear on whether you're referring to voltage applied or the amp-hour capacity that you push the battery to. How does one know when they've over charged the battery to an ample degree without going too far with it?

I'm not a fan of adding epsom salt to batteries to revive them as the chemistry doesn't make any sense - meaning there is no chemical mechanism at play to allow it to do what is claimed - but what you did in terms of replacing the electrolyte does make sense. I have to say I haven't tried this before but it sounds like what you did is very similar to what some industrial battery recovery businesses do. How to properly reform it back into a traditional lead acid battery? I'd have to do some research as I admit I don't know how.

Thank you!

Once removed from the charger the battery stops desulfating. Nothing happens when sitting static. You're free to let it rest for 10 hours but it's just wasted time.

@@knurlgnar24 thanks for your reply. First of all I need to say that I missed part 1 of your video and didn't realize what kind of battery did you used and general idea of that video (battery restore process). But what situation for a little bit sulfated battery which well maintained before? I'm not really sure it should be cycled that way, am I wrong?

Most of the lead sulfate is retained by the plates and stays in place, but some plate shedding does occur whenever a sulfated battery is recharged. All flooded batteries are designed with plates that have empty space at the bottom of the cells to allow this shedded material to collect without shorting out the active plates. Longer life batteries have more space than shorter life ones, but they all have this feature to some extent. For most people I take the stance that it's best to just let the shedded plate material settle to the bottom and not worry about it. Industrial battery restoration companies do flush that material out before selling them as used batteries but as this requires disposing of lead contaminated acid and reintroducing pure acid in the proper concentrations I just don't see it being practical for the typical individual.

> Dead is not great, especially for long lengths of time, but charging them to a negative voltage is MUCH MUCH worse. Can you further elaborate on this to someone who isn't an EE?

@@HaploPrime It has to do with the chemistries involved in some types of batteries. In the case of lead acids (car starter batteries) leaving them at exceedingly low charge for any period of time causes sulfation on the lead plates, usually rendering at least one of the six cells virtually or totally inoperable. In other chemistries, like NiCads, there are chemical processes when charge is reversed (happens when a cell in a pack loses capacity) and/or when the pack is discharged under load to extremely low voltages. In that case chemistry the cell is not designed to operate with occurrs, usually leading to irreversible damage, like some chemical bond occurring that is very hard to break. You can sometimes fix this to some extent, but the cell will probably never be the same. This is why cells are carefully matched for capacity for a given pack, but by definition there is ALWAYS a weakest soldier, and he will get felled first. If you don't deep discharge (quit discharging at the recommended pack voltage and recharge) this problem can be avoided, at least for the normal expected charge/discharge cycles, in that case about 1000, but I have had battery packs go FAR longer than that. Ni Cads can be stored almost indefinitely fully discharged, from my experience, but just one reverse charging will degrade a cell significantly, a few times will destroy it, and it will have virtually no capacity. Li Ions I don't know all that much about, but IIRC they are not supposed to be discharged below 1.1 V for a given cell. I also understand that in a hybrid or electric car battery, for instance, charging them to about 85%, and not letting them discharge below about 15% of recommended, AND keeping the cooling fan filters changed or cleaned regularly will VERY MUCH extend the life. You can probably get more/better info searching the web. I am certainly no battery expert, not even a little bit, but that is some of what I have found and/or understand to be true. Hopefully I got it right. NiCads and lead-acids I'm pretty solid on, some of the later technologies not as much. Hope this helps.

Lithium batteries are quite a bit different and cannot be recovered this way. There are different methods I have seen to partially recover them which I have not attempted, however I have not found any reputable sources that indicate they can be safely and effectively recovered once they have been damaged or aged. Unfortunately my current opinion is that bad lithium batteries should be recycled and replaced.

@@knurlgnar24 OK, I will follow your advice, they aren't all that expensive anyway to replace. Damaging them can be quite risky and I do not want to breathe lithium gas anyway. Thanks!

Wish I had known that. ;) There are industrial battery re-conditioners who use similar processes. They often also change out the electrolyte and such in some valuable batteries. A quick search for used forklift batteries should show who does that in your area. As shown here there's no magic to it and one can do this themselves with a little know-how.

Sulfated batteries will always have some permanent damage as a result of the abuse they sustained but any used battery will have some level of damage just from being used. Previously sulfated batteries that are desulfated will not re-sulfate faster than any other battery. Some people claim the sulfate crystals are nucleation points for new sulfation but I've not seen that borne out in any real world applications I've come across. Just take care of them like you would any other battery and they'll give you good service.

@@knurlgnar24 Alright awesome thanks for your reply

If you get old car batteries make sure they have the proper water level before doing anything else. I wish you well in your project!

@@knurlgnar24 Yes of course . I already tested a small bat that had only 2V and after adding some distilled water it came to 4.3v without any charge and it has lied like this for 4 days and still hold the 4.3V . Will put it on charge as soon I get a god weather ( dull rainy weather at the moment ) I will force 20V at 6A from solar panels .So I need sun lol. Thanks for your reply

Lead calcium batteries as well as pure lead will usually sit at a much higher voltage when fully charged. 12.8V does NOT mean fully charged in many cases. The 12.8V rule of thumb applies to lead antimony much better and is frequently stated simply so that people don't complain about their battery not being fully charged. My pure lead batteries sit at nearly 14V for months after being disconnected.

@@knurlgnar24 well I've had a lot of (and I mean a lot!) experience with lead type batteries and I've never seen any one of them that sits above 13v after resting fully charged. that small agm battery you're testing will rest at 13v at best when it's brand new. now I don't know if your "pure" lead acid batteries are any different (which I highly doubt) but there is no such thing as 14v resting OCV in LC batteries. it's maybe 13.2v at best. nothing more than that.

The useful Ah is different depending on the discharge rate. I showed this chart in part1 of the video.

It depends on how healthy the battery is otherwise. Some last only a few months, others last for over a decade. If your battery was 'new' and just sat on a shelf then you'll likely get nearly the full lifespan out of it. If it was heavily used and then got sulfated then it's probably not going to last very long.

I also should mention that desulfation only helps sulfated batteries. This is obvious but often overlooked. If the battery has other issues then this procedure isn't going to help matters. Batteries age and degrade over time and use and nothing short of recycling them can bring them back to a useful state at that point. A good number of batteries go to the recycler that are simply sulfated though and that's a shame.

Thank you for the wonderful advise and help. @@knurlgnar24

That's a 'dirty' way to do it, but it can work. It will NOT desulfate a battery by itself though as much more time is required. That procedure will only recover a battery just well enough for it to start taking a charge from a charger.

They way they work is that you set a 'voltage limit' and a 'current limit'. If the current the load is drawing is below the 'current limit' the power supply will increase the voltage it supplies in an attempt to increase the current until the 'voltage limit'. If the 'current limit' is exceeded the power supply will reduce the voltage it is supplying in an attempt to reduce the current all the way down to 0V if necessary until the 'current limit' is no longer violated. All lab supplies work this way.

@@knurlgnar24 thanks for response man your units $90 now bit there are others for less just didn't know if they would work the same

Thanks I purchased the 30v one you shared have trouble getting to stay on cv like you did in the video, sure it just a learning curve. Saved one battery working on a second but it might not work one cell smoking and getting hot was hoping it would stop but no luck yet

I was going to use my conductance meter but the video was getting so long I omitted it. Now I wish I hadn't.

@@knurlgnar24 Well, just post a final reading here. (24 hours after full charge)

I did not and yes water can be added to the glass matts. I don't recommend this for various reasons but if the cells are low on electrolyte then adding water will help.

@@knurlgnar24 I understand the not recommending it on here. I have several full river agms I've been using in a off grid solar system for about 8 years. I've brought back several Small inexpensive AGMs by either adding water to the matt or pulse charging but I don't have those awesome toys you have for checking the ah and such. I wonder if the cycle life the factory puts out is the actual lifespan or if by desulfating and adding electrolyte can get far more life from them. What you say to this question? Awesome videos BTW.

The surface charge certainly contributed but it would only affect such a test by a few percent. Now years after this experiment when I look back it's pretty clear that battery temperature was the only significant factor. I was thinking of covering this in a new video at some point.

@@knurlgnar24 Was the temp factor good or bad?

I suppose that is one solution!

The cells probably shorted out, how old is the battery? What SG in bad cells?

As I understand things, it would show 12 volts if a cell is shorted. It's a pretty old battery but the vehicle was not used for several years. That's it's problem, discharged too long and sulfated. I don't have an exact SG figure, just 25% of charge.@@SinsBird

​@@TomDay-dt7ne The open circuit voltage on a fully charged battery should be at least 12.6 volts sulfated or not. Charge at 2-3 amps for 2 hours a day, then let it sit until next charge. Before every charge measure and write down the specific gravity of each cell. Add 10 ml or 0.3 oz of water if specific gravity is higher than 1.27.

Correction - I meant to write "it would NOT show 12 volts if a cell is shorted." @@SinsBird

@@TomDay-dt7ne Yes, I understood that.

Simple off-the-cuff thought: Connect a bunch of them up in parallel and force 0.5A through them (if 10 batteries 5A) for x hours depending on their condition. I'd do more than 4 at a time personally. Check the status with a DMM and conductance meter. Sort and continue. Sounds like a fun project.

You're not missing anything. The situation is that discharging to 8.5V would have made very little difference vs 10.5V.

The ideal load level depends on the battery size but really your patience is the limit. Any load will work. Put it in your car and turn on the headlights, find a 12V appliance and connect it to the battery, etc. An electronic load is a luxury. I think everyone should have a cheap 12V to 120V inverter for emergency situations so that's what I'd suggest. Even a $20 one would charge your phone, run your laptop, run LED lights, let you watch TV with physical media, etc and be pretty useful for power outages, camping, traveling, etc.

If your batteries are only 6 months old it is pretty much a guarantee that they will recover to near 100% with the method shown in this video. Irreparable sulfation damage take more time than that. I am not surprised that the NOCO charger didn't work - that isn't a negative comment on that particular charger, just a comment in general on the state of chargers today.

A battery that settles to 12.7V after a few days is a damaged battery (lead antimony chemistry excluded). Any good battery should stay above 13V for a long time - usually months. I do agree that this battery may have lost some water.

Probably too much voltage for a 12V battery and voltage regulation isn't their strong suit, but depending on the welder it may work.

AGM batteries bubble just like flooded lead acid except that the bubbles are slowed down by the fiberglass mesh. The idea is that they are slowed down enough so that the hydrogen and oxygen recombine into water before escaping out the top of the cell. Overcharging doesn't cause issues unique to AGM batteries aside from pressure which could deform or rupture the case if the bubbling is violent enough, or more likely simple dry-out due to electrolyte loss.

Awesome! Now I have 2!