Attempt 'rejuvenating' old gel-cell lead-acid batteries with a bench supply? - Page 1
Forum section: electronics / repair

author: cdev
author_rank: Super Contributor
timestamp: November 23, 2018, 01:09:55 am
content: I have a bunch of old gel-cell batteries that all show voltages well below 12v.Ive attached them at regular ijntervals to a cheap trickle charger meaning to try to rejuvenate them at some point. Now I am trying to declutter. Either I can fix them or I need to recycle them.For years Ive been hearing that various techniques existed to desulfate them.I've read all sorts of advice on this. But only had nice bench supplies accessible to me recently.There is no time like the present.What are peoples experiences and what can I do to try it using a bench supply with adjustable current?Is there any danger to the bench supply from doing this? Most of these batteries show voltages of 6-11 volts now. Some are lower.They are gel-cell batteries like the ones from UPS's.

author: BradC
author_rank: Super Contributor
timestamp: November 23, 2018, 02:01:49 am
content: Quote from: cdev on November 23, 2018, 01:09:55 amMy experience? You will spend quite a bit of time learning that it's a relatively futile effort.I won't say you are wasting your time, as time spent learning is never wasted.My experience is that SLA batteries are generally a lost cause.*Quality* batteries (like Japanese made Yuasa) can often be brought back from the dead if they have died from sulfation, but only at a fraction of their original capacity. Cheap Chinese SLA's generally don't come back to any meaningful capacity.You won't damage your power supply, but you may well spend a lot of time reaching a similar conclusion. I've tried all the magic chemical tricks, and all the whizz-bang electronic de-sulfation techniques and am yet to find anything that actually works. Most SLAs I come across have died due to plate corrosion, which is a combination of time, float voltage and cyclic use. They have a limited life-span which is specified under best case conditions, and I've never found a device that maintains them at those conditions, so they all die faster than their design life.I have some fabulous CSB 7AH batteries here that will still start a 4-stroke generator (so their impedance is still nice and low) but they are down to about 2AH at a 20C rate.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 23, 2018, 02:36:31 am
content: BradC said it well. My experience also. Either recycle them or repurpose them. I use them for weights when glueing things and other similar uses.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 23, 2018, 02:49:12 am
content: If you're not getting any current into them at 14.3V (or whatever the exact float voltage is for that type), they're dead dead.AFAIK, the mechanism is sulfation cutting off current flow. Sulfation is the state of full discharge, and something something crystal growth making it that much harder to get a charge going again. Lead sulfate is an insulator.The way electrochemistry works, or a lot of it anyway, is electrons being forced into or out of solution at the electrode surface. These immediately form ions, radicals, whatever. Example, there's organic chemistry that can be done with electrochemistry (I forget what; I think one is a radical decarboxylation, which turns two molecules of an organic acid into a paired up backbone, with the loss of two CO2's, probably as CO3(2-) in solution?).So, lead sulfate being an insulator, it probably doesn't participate directly, and it has to be in a very small, thin form near the electrode surface, where it can be attacked by the ions and radicals at the surface, without having secondary reactions take over (namely, electrolysis of water -- loss of electrolyte volume, no actual charging). Or it's a thin film, nanocrystalline or amorphous maybe, which is conductive over that distance (or capable of tunneling, say). (Now I'm getting curious, and I wonder if there's an article that studied this?)In any case, big crystals of the stuff, don't participate, or at least not very much. And the more sulfate there is blocking off electrodes, the higher the internal resistance. Which means not only is discharge current minuscule, but charge current as well.And, low current means low charge rate.The best you can do, AFAIK, is to float for an extended period of time (days, weeks... months?), at just enough voltage to effect the charging reaction, without causing electrolysis. This doesn't leave much excess voltage to drive the reaction forward, and we're talking about large crystals not fine deposits, so it could take very long indeed.In time, hopefully, the ESR falls, the charge capacity rises, and sulfate is reduced, at least the sulfate still sticking to the electrodes. Hopefully any shedded sulfate, sitting at the bottom of the cell, isn't reduced and causes a short.I'm not aware of any mechanism or science behind the more fringe recovery methods. Surge voltage/current might be able to open up a shorted cell (preferably, applied across the cell in question, not the whole battery), but that's only a temporary trick. I don't know that applying a large voltage (in either direction) would be able to, say, shake loose some sulfate. Electrolysis -- producing bubbles -- might be able to shake some things loose, but this disturbs the metal sponge as well, also not recommended.Mind that, of course, the stuff-moving-around only applies to a regular lead-acid, not a gel-cell. Hopefully the gel will hold things in place better, but who knows how much can be recovered if any. Definitely don't overvoltage them, which makes gas that doesn't have anywhere to go (or, I guess there's a catalyst in there to consume modest rates of gas, but not large amounts!).Tim

author: BradC
author_rank: Super Contributor
timestamp: November 23, 2018, 03:36:48 am
content: Quote from: T3sl4co1l on November 23, 2018, 02:49:12 amAs with all sealed cells, there is definitely a catalyst. If you pry the plastic top cover off the battery you'll see little rubber caps sitting over plastic pipe-spiggot thingies. These are actually relatively well calibrated pressure relief valves, and when you exceed the capacity of the catalyst to recombine the gasses you'll hear the battery fart as the cells push gas past the rubber caps. It can be quite disconcerting the first time you hear it happen, particularly when it's a relatively healthy battery that is being grossly overcharged and you hear all 6 cells popping off at random intervals.The common internet "wisdom" is to take the caps off, poke a couple of drops of water back down there and put it back together again. The trouble is if you've been gassing the battery sufficiently to lose enough water to warrant doing that, you'll have caused significant plate corrosion and knocked a heap of capacity out of the battery in any case.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 23, 2018, 05:18:39 am
content: One trick for reconditioning lead acid batteries involves a light dimmer set to about half, a mains rated capacitor (value depending on size of battery, 5-10uF motor run cap good for a car battery), and a bridge rectifier. Basically a crude pulse charger.

author: tautech
author_rank: Super Contributor
timestamp: November 23, 2018, 06:50:39 am
content: Good luck, cut your losses or spend an unhealthy amount of time trying to recover LA batteries.Like pushing the proverbial uphill with a pointed stick !Went down this path ~15 years back and built and optimized a few desulphators the best of which was quite simple and was powered from the battery itself. Pretty neat to see battery voltages rise after an overnight zapping from 7A, 65V @ 1KHz however any significant capacity gain was always illusive and I now only consider desulfphation only as a LA battery maintenance exercise.Better and more cost effective to properly manage and maintain batteries rather than try and shut the door after the horse has bolted !

author: RoGeorge
author_rank: Super Contributor
timestamp: November 23, 2018, 07:04:56 am
content: Quote from: BradC on November 23, 2018, 02:01:49 amSame here. Once damaged, those UPS batteries can not be recovered. The best thing to do is to discard them at a recycle center.

author: Circlotron
author_rank: Super Contributor
timestamp: November 23, 2018, 07:41:06 am
content: Back in the early 90s I worked at a place that had a small warehouse full of UPSs, many of which had sat around for 4 or 5 years just waiting to be sold. They had 12V 6.5Ah and 24Ah batteries that typically measured about 2 volts. They would put new batteries in them before they were sold, so I had way heaps of batteries to experiment with.The technique was refined to the following:Reverse charge the battery at 2% of its Ah rating for 48-72 hours.Then forward charge the battery at the same rate, again for 48-72 hours.Absolutely under *NO* circumstances crank up the charging current!!! If you do, you will find one cell will get hot and then it’s all over, red rover. It’s junk.Recovered many batteries that way including one 24Ah that I put in my Daihatsu Charade and it would easily crank it for several minutes continuous. Didn’t try to see how long till it quit.So it can be done with batteries that were once good but just sat around for a long time, but as for old worn out batteries, I don’t think so.

author: RoGeorge
author_rank: Super Contributor
timestamp: November 23, 2018, 11:43:32 am
content: Quote from: Circlotron on November 23, 2018, 07:41:06 amNever tried to reverse the polarity when charging a UPS battery.Just to be sure I understood it correctly, let's take an example:- take an old gel battery 12V/7Ah. Measure the voltage with the battery disconnected. It should be at least 2V to be good for a recovery try.-charge it in reverse polarity at a current of 140mA for about 2-3 days. After this, we expect to have the voltage reversed, so the red terminal is now the negative of the battery, and the black terminal is the positive one.-charge with normal polarity atthe same 2% current, in this exampleabout 140mA for another 2-3 days.After this, the battery might work again. The recovery is not guaranteed for each and every battery, but some of them may be restored.Once a recovery is successful, from now on we can use the battery at normal charge/discharge rates, without the 2% current limit, and without reversing the polarity at each recharge.I'm curious to give this a try with the first occasion, did I understood the procedure correctly, please?

author: Circlotron
author_rank: Super Contributor
timestamp: November 23, 2018, 12:05:30 pm
content: Quote from: RoGeorge on November 23, 2018, 11:43:32 amYep, 100%.When charging reverse direction, have the charger set so the voltage won't creep up any higher than 13.65V for a 12V battery, same as a normal charge. And like I said, DON'T wind up the charge current!

author: Rascal
author_rank: Contributor
timestamp: November 23, 2018, 01:25:04 pm
content: I was given one of those 12v solar panels advertised for car/boat/camping, and I often use that to attempt to rejuvenate old gel cells. I attach it and leave it for a few days to work its magic. Occasionally a few days may turn into a week or two if I forget.More often that not the batteries appear to recover (certainly to some extent) I will quite happily use them.Paul

author: CJay
author_rank: Super Contributor
timestamp: November 23, 2018, 02:32:54 pm
content: It can be done but it's unlikely you'll get full capacity.I have had success and have measured (crudely) capacity at a fairly high percentage of original spec so those batteries were useful, others, not so much, you'll also need to test them on load if they appear to recover as I've had a few which looked great but just couldn't sustain the current drawn.My recipe for 'success' is to give them a few solid thumps, base flat down onto a lump of wood, if you meause the current draw before and after you can often see an immediate increase, I guess it shakes loose sulphated material from the plates.The Yuasa batteries seem to recover fairly well, charge at 13.5V for a 12V battery and watch the current as well as the battery temperature, it takes patience.If you're expecting to get long life out of them, forget it and buy new, if you're only using if for non critical applications or just to see if it can be done then it might be worth the effort.My absolute favourite lead acids are Hawker/Gates Cyclon, I've seen them recover from 0V terminal voltage to almost 'as new' capacity, excellent quality cells.

author: cdev
author_rank: Super Contributor
timestamp: November 23, 2018, 05:20:18 pm
content: Circlotron, thank you for this great info!I think I saw one of your earlier posts. Thank you!Your process is what I wanted to try out. Since I would just throw them away anyway.Okay, I am going to try this on a dual cell gel-cell I have here - maybe a 7 ah gel cell, which is currently only delivering 4.5 volts. Its at least eight years old and was used in an alarm system until it died, then was used for low current stuff intermittently. I'm going to see what my bench supply does when I connect it upin serieswith it with the current limiting set to 150 ma.. Luckily the bench supply is built like a tank.What should the current be set at for different size batteries?This is likely a process that would lend itself to optimization.I have a bunch of different ones in different sizes.I even have one old car battery, in a similar state of age. It was used in a car until it was retired around two years ago. Since then Ive kept it topped off with a trickle charger that was never meant to actually put the main charge on a battery, just keep it topped off. Now its showing 11 volts.My bench supply can deliver up to 20v at 3 amps (x 2) So charging the car battery at after it recovers could be done, up to 3 amps - but probably best to try less, and also a reasonable voltage, no more than 13.6 volts? Its really cold today, and the cold has even inflicted the indoors. Outside its well into the negatives, way below freezing.Ever since I read your original post Ive wanted to try this out.Do I need to put it in a metal tray or something? Or do this in the basement? I would hate to have it explode on my dining room's nice hardwood floor! But also good to have it close by so I can keep an eye on it and check on it. Maybe I will do the car battery in the basement, and do both in a metal tray.Quote from: Circlotron on November 23, 2018, 07:41:06 amThis is a semi worn out battery, I suspect. But what the hell.Cheap thrills!

author: tautech
author_rank: Super Contributor
timestamp: November 26, 2018, 09:11:35 am
content: Quote from: Circlotron on November 23, 2018, 07:41:06 amI've just got the perfect candidate to try this ^ !A 12V MOTOBATT AGM 20AHrhttp://www.motobatt.com/MBTX20UCCA 310A, Capacity (10HR) 21 AHr~3years old from a neglected jetski score !Free standing open circuit voltage 1.7VA previous quick look at this battery a few days ago to see if it would take a charge was done with a reasonably modern LA charger that needs a residual voltage before it will charge and of course this battery wouldn't. Another dumb LA charger was connected also to bump the voltage up to where the smarter charger would latch and commence charging but when removing the 'bump' charger, charge was not maintained.Normally I'd give this one up as stuffed but the case looks perfect without any swelling/bulging.Circlotron battery recovery method.Started NZ time = ~10pm 26 Nov.2% x 20AHr =400mA reverse charge from a CC supply set to 13.8V, CC'ed down to 1.6V......will this work ?Will check it several times/day and make any necessary adjustments if/when required.Supply: MCH K305D (30V 5A SMPS) All charge voltages and current noted from the PSU display readout.Discharge voltage and current measurements: Fluke 15B and Kaise analog meter.The clock is ticking !Reverse charge progress log:ALL charging measurements .....PSU set to 13.8V and in current controlled (CC mode)Measurements from PSU display readout unless otherwise specified.0 hrs. Voltage 1.6V @ 400mAreversecharge.10 mins Voltage 1.4V15 mins, Voltage dropped another 100mV to 1.3V.20 mins, Voltage 1.2V,2 hrs. Voltage 1.0V, Battery cool to the touch.7am 27 Nov9 hrs. Voltage 1.0V. Current 400mA stable and battery cool....no warm spots.10 hrs. Voltage 1.3V.11 hrs. Voltage 1.8V.12 hrs. Voltage 2.4V.14 hrs. Voltage 2.9V17 hrs. Voltage 3.2V.18 hrs. Voltage 3.7V. Current stable @ 400mA. Temp slightly above ambient, no hot cells.19 hrs. Voltage 4.2V. Ever so slightly warm, will watch this closely and maybe reduce reverse charge current.22 hrs. Voltage 5.5V. Still watching temps, no change from before.23 hrs. Voltage 6.5V. Confirmed polarity reversal with a DMM.24 hrs. Voltage 7.5V Temp and current stable.At the speed of reverse charging now I'll back off the current to 300mA until the morning when I can keep an eye on it every couple of hours.Then I'll wind it back to 400mA and let it stabilize for a bit before continuing this log.7am 28 NovAfter overnight reverse charging at the lower 300mA rate the battery was quite cool and @ 9.5V.33 hrs. Voltage 10.3V. Reverse charge returned to 400mA.34 hrs. Voltage 10.7V.35 hrs. Voltage 10.7V. Interesting, have we reached some plateau ?36 hrs. Voltage 10.7V. Battery still cool to the touch. PM sent to Circlotron for advice and Amps reduced to 100mA while I await his reply. 9.6V (slowly falling) @ 100 mA........7.7V now ~15 minutes later.37 hrs. Voltage 8.1V @ 100mA with a still reversing charge.38 hrs. Voltage 8.9V @ 100mA. With reply from Circlotron I'm lifting charge to 200mA (1% of C) to observe battery behavior.....9.4V. Will probably lift current more in another hour or so.39 hrs. Voltage 10.2V @ 200mA reverse charge. (1% of C)40 hrs. Voltage 10.3V. Current lifted to 300mA.....10.6V. Battery @ ambient temp.41 hrs. Voltage 10.7V @ 300mA. Will it go higher or have we reached the 10.7V plateau again ?42 hrs. Voltage 10.9V @ 300mA.43 hrs. Voltage 10.9V @ 300mA.45 hrs. Voltage 10.9V @ 300mA. Battery slightly warm. Will run until the morning, say ~56 hrs then leave to settle and measure OC voltage before deciding if more reverse charging needs be undertaken or to start the discharge prior to forward charging. Much will depend on results from another overnight reverse charge.48 hrs. Voltage 10.9V @ 300mA. Battery slightly warm. Plan is to do some OC voltage measurements over maybe 30 minutes while the battery stabilizes before draining it prior to the forward charge.Will also log the discharge which might at the end be able to indicate the success of this attempted recovery...or not. Till the morning....10am 29 Nov60 hrs. Voltage 11V @ 300mA. Reverse charge terminated.Open circuit voltage after 10 mins 8V.Nearing a stable but 'reversed' voltage 7.5V ~20 mins after reverse charge terminated.7V and still very slowly falling.6.75V and nearly stable reverse voltage.Discharge commenced.11.35 amLoad: 30W 12V sealed beam spotlight, 2.25A measured draw @ 13.2V.Actual battery drain 1.3A+10 mins 1.16A, 3.7V+15 mins 1.13A, 3.3V+20 mins 1.1A, 3.15V+25 mins 1.08A, 3.1V+30 mins 1.05A, 3V+35 mins 1.01A, 2.75V Starting to noticeably fall away.+40 mins 0.95A, 2.4V+45 mins 0.88A, 2V+50 mins 0.8A 1.55V+55 mins 0.74A 1.2V+60 mins 0.69A 1.0V+65 mins 0.64A 0.8V+70 mins 0.6A 0.7V+75 mins 0.55A 0.55V+80 mins 0.5A 0.45V+100 mins 0.25A 0.2V+110 mins 0.21A 0.15V Battery now resting to observe any recovery....immediately to 1V then to 1.75. Will rest a further 5 mins......2.45V.Further discharge started.+15 mins 0.17A 0.125V+65 mins 0.09A 0.06VForward charge commenced.3pm 29 NovTarget = ~13.8V with charge current falling indicating battery fully 400mA (2% of C rate) trickle charged.0 hrs. Voltage 1.3V @ 400mA+20 mins Voltage 1.5V+45 mins Voltage 1.8V1 hr Voltage 2.0V2 hrs Voltage 2.5V. Battery temp barely above ambient.2.5 hrs Voltage 3.0V3 hrs Voltage 3.2V4 hrs Voltage 3.8V5 hrs Voltage 5.0V6 hrs Voltage 6.5V7 hrs Voltage 8.0V @ 400mA Reduced to 300mA for overnight. Battery cool.12 hrs Voltage 10.2V @ 300mA14 hrs Voltage 10.4V @ 300mA15 hrs Voltage 10.5V23 hrs Voltage 10.6V @ 300mA. Charge rate increased to 2% of C: 400mA = 10.9V.26 hrs Voltage 10.8V @ 400mA.27 hrs Voltage 10.7V. Battery barely warm.30 hrs Voltage 10.7V40 hrs Voltage 11.0V @ 400mA41 hrs Voltage 11.1V43 hrs Voltage 11.2V@ nearly 44 hrs....75 min power cut. Measured OC battery voltage 11V. 1 hr later 10.8V.Forward charge resumed (45 hrs) 1 pm. Voltage 11.0V @ 400mA.46 hrs Voltage 11.3V47 hrs Voltage 11.4V56 hrs Voltage 11.8V. Still @ 400mA and battery still cool.65 hrs Voltage 12.1V66 hrs Voltage 12.2V70 hrs Voltage 12.3V73 hrs Voltage 12.4V76 hrs Voltage 12.5V78 hrs Voltage 12.6V87 hrs Voltage 13.1V88 hrs Voltage 13.2V89 hrs Voltage 13.3V90 hrs Voltage 13.4V91 hrs Voltage 13.7V CC'ed voltage rising quite quickly now as we approach the 13.8V PSU setting.Expecting to see the current (400mA) start decreasing soon after 13.8V battery voltage is reached.~92 hrsMidday Dec 2Target voltage (13.8V) reached with battery draw current quickly reducing .....now 340mA.93 hrs Voltage 13.8V Current 230mA.~30 mins later current 180mA.Will leave charging @ 13.8V CC until no further current decrease is noticeable, then rest battery for an hour or so to get a stable OC voltage before attempting any discharge/capacity tests.~95 hrs Voltage 13.8V @ 120mA.From discussion in reply #33 charge voltage has been lifted to 14.5V where current increased to 250mA and falling reasonably quickly. In just a few minutes down to 200mA.I'm calling recovery forward charge finished at this time as the little further charge can/will be added to the battery. ie. insufficient to make any significant difference to upcoming load/capacity tests.3.15pm Battery resting.+5 mins OC 12.75V+15 mins OC 12.64V+30 mins OC 12.6V1hr OC 12.56VDischarge log 4.50 pm.OC voltage 12.54VLoad: 12V 30W handheld spotlight.Drawing ~2.2A battery voltage ~12.3VAttempting a dual measurement histogram with SDM3065X bench DMM........+30 mins Voltage getting close to 12V and current just over 2A.+50 mins Voltage 11.9V Current 2.07A2hrs Voltage 11.78V Current 2.04A3hrs Voltage 11.6V Current 2.01A4hrs Voltage 11.38V Current 1.99ADischarge stopped. Battery recovered to 11.62VBattery returned to charge, target = 14V @ 1A CC (5% of C)0hrs Voltage 11.9V @ 1A9hrs Voltage 14.0V @ 0.1ACharge stopped.+2hrs static voltage 12.54VInitial/preliminary findings/summary.~40-50% of battery capacity recovered from this method.UnknownsWill this battery hold charge for any useful period ?Will these initial battery test results improve or degrade with further use ?Further battery conditioningMaybe some time on the desulphator built many years ago.TBC..........Please note: ongoing edits throughout this post for text clarity and better understanding.

author: Circlotron
author_rank: Super Contributor
timestamp: November 26, 2018, 10:20:45 am
content: I was thinking - when the time for reverse charging is up, discharge the battery down to zero before connecting to the psu for charging in the forward direction. If you don't do that, the battery supplying reverse voltage to the psu may damage it. Lots of current may flow through the rectifier diodes, filter choke and transformer secondary.Apart from that, keep us posted!!!P.S. You should live-stream it on YouTube :-)

author: RoGeorge
author_rank: Super Contributor
timestamp: November 26, 2018, 11:34:57 am
content: About the safety of recharging batteries using a generic lab power supply, it's a good practice toput a diode in series with the battery you want to charge. Many power supply have a crowbar circuit that shorts the output of the power supply when the voltage is bigger than what the power supply expects it to be. This can happen by accident, or during a power outage. Another reason is that a charged battery can deliver strong enough currents to melt wires and start fires. If something goes wrong inside the power supply, and the output of the power supply short circuit itself, we'll also get a short-circuit on the battery we charge. This can start a fire.I always put a series diode when using a lab power supply as a charger. For my particular case, 2xST double diodes recovered from defective PC power supplies on a former processor radiator acts not only as series diode, but they put in parallel the 2 channels of a Rigol DP832 power supply for a bigger current when recharging a car battery. In the user manual of DP832 is specified the series diode as mandatory when using the power supply as a charger.

author: duak
author_rank: Super Contributor
timestamp: November 26, 2018, 06:38:14 pm
content: I agree that it's a good idea to have a series diode to protect the power supply. Even if the supply doesn't have overvoltage protection, it may be sensitive to voltage on its output. For example, the Lambda LP-41x series utilizes a floating regulator design where the output voltage is determined by a variable resistor to the negative output. If this resistor is turned to low resistance while the output voltage is held high, protection diodes in the regulator conduct and send excess current through the resistor and either damage or destroy it. Quite a few other power supplies use a similar design, (hp in particular) and I suspect could be damaged too.I whipped up a rejuventor using an 80 V supply, a capacitor bank and a power MOSFET switch to apply short high voltage pulses to the battery. If the battery isn't too far gone, it'll often regain some capacity but it's only a temporary fix. If more than one cell was heavily sulfated, nothing helped no matter how long I left it on.Cheers,

author: cdev
author_rank: Super Contributor
timestamp: November 26, 2018, 07:07:07 pm
content: I'm glad you posted this because I am doing this as we speak.I am not sure if I am seeing a crowbar activating or current limiting in my power supply. Because only 13 ma is flowing.I am using a generic switching diode in series with the power supply.I needed to verify the current limiting set point before starting - which I use an 8 ohm power resistor to do. I just did this again to verify that my power supply is not broken. Its not.When it is just connected to the resistor, it gets hot, unless I set the current limit to whatever.A crowbar may be acting to prevent my reverse charging the battery?Trying to Google for that now. Themanualdoes specify that one needs to use a fuse when using it to charge batteries.There is no indication on my supply of any crowbar operation.Normal operation is in constant voltage mode which displays a green LED.Besides the current meter (digital) a red LED goes on when it current limits, it is currently off.But it says nothing in the documentation about any crowbar indication if you don't have one of the add on interface cards it can be upgraded with. (I don't) I do think they indicate it.I doubt if there is anything I could throw at this power supply that would damage it.Its a real beast. But it is quite possible it could and would self-limit.Its more than 30 years old, but its still a current model, its still being sold. Which must be some kind of record.

author: Gyro
author_rank: Super Contributor
timestamp: November 26, 2018, 09:37:59 pm
content: If all else fails, the scrap value of LA batteries is quite high. Check your local metal recycling company (not sure where on the planet you're located).

author: cdev
author_rank: Super Contributor
timestamp: November 26, 2018, 10:28:34 pm
content: I could charge a large electrolytic capacitor.How much voltage for 12 volt cells, and do you apply it in the forward or reverse direction?Quote from: duak on November 26, 2018, 06:38:14 pm

author: tautech
author_rank: Super Contributor
timestamp: November 26, 2018, 11:08:46 pm
content: Quote from: Circlotron on November 26, 2018, 10:20:45 amYes I wondered where voltages and battery energy would be when we are ready to start the forward charge....I'll keep your comments in mind however there's a lot of battery behavior to record yet as we go through your recovery process. I haven't got a programmable load (Siglents one is not released just yet) however plenty of various wattage auto bulbs and 12V spotlights to drain the battery to nearly zero before we start the forward charge. Fingers crossed !I'm not looking to continually create new posts instead opting for ongoing edits in reply #14 to record it all in a single post.Starting to see a trend of rising reverse voltages now as the battery starts accepting the reverse charge.

author: floobydust
author_rank: Super Contributor
timestamp: November 26, 2018, 11:10:38 pm
content: I askedwetlead-acid car battery "rebuilders" what they do, they replace the electrolyte with some special reconditioning Battery Chem or Epsom salt and then charge at the highest rate the battery can take, say 50A to break off the sulphate crystals. The battery is literally boiling and it's limited by temperature rise. They must save enough batteries to make a profit.I think reverse-charging is silly. Sulphate crystals are very tough and I've never been able to do much with them regardless of time, current, polarity on lead-acid batteries.Desulfators really need to hit the cells hard:https://www.eevblog.com/forum/oshw/desulfate-regenerate-lead-acid-batts-a-new-diy-guide-overnight/https://www.eevblog.com/forum/projects/guess-what-will-happen-battery-desulfation-experiment/Even then, lead-acid batteries are basically always corroding when not charging, it's lead in sulphuric acid and the metals breakdown so no repair is possible:http://everist.org/NobLog/20180430_lead_acid_ruin.htm

author: Bud
author_rank: Super Contributor
timestamp: November 27, 2018, 01:50:30 am
content: Quote from: CatalinaWOW on November 23, 2018, 02:36:31 amThat is what i use them for, too. They also double as weights for exercising.

author: duak
author_rank: Super Contributor
timestamp: November 27, 2018, 02:58:55 am
content: cdev:I applied the pulses to the battery in the forward direction. The voltage was pretty much 80 V. The capacitor bank was a few thousand microfarads of lowish ESR 200 VDC caps pulled from PC power supplies. I initially tried to use an IRFP340 FET as a switch but it couldn't handle the current for bigger batteries. I had some bigger STM FETs rated for a 100 A and 100 V. I used a pulse generator to drive the gate at 10 to 100 Hz with a pulsewidth of 50 to 500 microseconds. As the sulfate is converted, the peak current goes up and the power supply loads down. If memory serves, I was getting 50 to 100 A pulses into a car battery.About applying a reverse voltage to a power supply. Many supplies have a diode on the output to limit the reverse voltage. What the supplies actually do when this happens depends on the design. I suppose some would be damaged right away, some would get really hot because the pass element has to dissipate more power than they were designed for and some might latch up. I would apply the reverse voltage to the battery thru a power resistor sized to allow the power supply to develop the correct polarity voltage yet still deliver the charging current.I haven't tried the reverse voltage bit, but it's an interesting idea.Cheers,

author: floobydust
author_rank: Super Contributor
timestamp: November 27, 2018, 05:44:01 am
content: Um, don't forget these old batteries make hydrogen gas which explodes easily, along with the sulfur stink.Any spark at the plates can make a bang, so I don't advocate massive overvoltage unless you've got safety glasses and a bin to contain the spray.

author: duak
author_rank: Super Contributor
timestamp: November 27, 2018, 09:48:24 pm
content: I'll echo what Floobydust says about hydrogen gas. I didn't do it with any of the rejuvenation experiments, but I did suceed in blowing the side out of an MC battery during quick charging. I was young and lucky.Cheers,

author: tautech
author_rank: Super Contributor
timestamp: November 29, 2018, 03:17:13 am
content: Hopefully on the home straight now with the forward charge now commenced. See reply #14 for the ongoing logging:https://www.eevblog.com/forum/index.php?topic=152765.msg1991789#msg1991789

author: Circlotron
author_rank: Super Contributor
timestamp: December 02, 2018, 11:50:51 am
content: Checking the results every few hours.Go, little battery! You can do it!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 02, 2018, 01:58:02 pm
content: Two FYIs:1. At 400mA, you're in basically no danger of heating up anything noticeably. You can hold 10V * 400mA = 4W in your hand comfortably, though in that size it will be noticeably warm. In a battery size, fuggeddaboudit.If anything's being damaged, it will be chemically, and not apparent until you've done full charge cycles. Examples: increased self-discharge, increased ESR (even at full charge), reduced capacity, poor capacity retention over time (maybe it's only good for a few dozen charge cycles after this; or maybe a thousand, good as new??).2. Give or take enough charge, a lead acid battery is symmetrical. Taking a reverse charge means you'vefully reducedthe lead dioxide cathode (if not in bulk, then at least the active surface), and are now producing hydrogen on it, while the other is being oxidized to lead dioxide (on the surface). Lead dioxide tends to expand and flake off the surface of a bulk lead electrode, so I don't know how healthy this will be to the "sponge" structure.So... we'll see what happens.Tim

author: cdev
author_rank: Super Contributor
timestamp: December 02, 2018, 01:58:15 pm
content: (You're adding the 0.6 volts or so voltage drop of the diode in series with them- right?)Quote from: RoGeorge on November 26, 2018, 11:34:57 am

author: tautech
author_rank: Super Contributor
timestamp: December 02, 2018, 11:09:23 pm
content: Quote from: Circlotron on December 02, 2018, 11:50:51 amIt's gunna ! !Just in the time to grab this pic and compress it for posting the charge rate has fallen to 360mA.Some battery rest to stabilize and load tests to come.But first....should we push the charge voltage a bit higher ?Battery seems quite happy and cool.Results to be documented in reply #14........

author: Circlotron
author_rank: Super Contributor
timestamp: December 03, 2018, 01:44:32 am
content: Yeah, 14.5V or so for half a day shouldn't hurt.As to how low you should let the charge current drop to, not sure. It may not drop to as low a figure as what a "good" battery would. Just have to wait and see.And that 13.8V is upstream of the diode of course, not the actual battery voltage...

author: tautech
author_rank: Super Contributor
timestamp: December 03, 2018, 02:03:49 am
content: Quote from: Circlotron on December 03, 2018, 01:44:32 amTBH I'm reluctant to push the charge voltage so high just yet.Sure that's just on the max of a cyclic charge limit whereas we've targeted the recommended max of a standby/float charge. It would appear that the battery is quite happy with the treatment it's been dealt so I'll maybe push the charge voltage to 14.2V (cyclic min) which going by recent behavior it should reach reasonably quickly. Further charge notes in reply #14.QuoteWe're down to 120mA @ 13.8V and charge current has slowed up dropping to the point where IMO it's mimicking normal SLA battery charging behavior.At this point I'm really happy with what I've seen and logged however as they say 'the proof is in the pudding' and some discharge/capacity checks will tell us a lot about if your process is really worth its salt !Now we have some logging about expected behavior the effort and process is relatively straightforward and almost 'set and forget'.Thanks for 'being there' and keeping an eye on proceedings.EditCharge voltage bumped to 14.5V and current has only risen from 120mA to 250mA......and falling.~3.15 pm @ 200mA recovery forward charge ceased.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: December 03, 2018, 08:52:33 am
content: A series diode will NOT protect a PSU from a reversed battery. Think about it for a moment: If the diode allows current to flow from the PSU +ve at 14v to the battery +ve, at say 13v, then it will also allow current to flow from the unpowered PSU (0v) to the (reversed) battery -ve at -12v. The voltage drop being in thesamedirection.It will prevent a short if the PSU 'crowbars' the output. I've met one or two PSUs like that and basically it's a braindead idea since the short on the output can also damage a downstream regulator through back current from filter or decoupling caps.To make a reverse polarity proof battery charger, you need an arrangement which will briefly tolerate reverse polarity on the output, and disconnect the output when that arises. If the PSU is current limiting itmaymeet the first criterion, depending on actual circuit, and a relay or mosfet can provide the disconnection. A horn with a series diode is also a good idea.Safetywise a gel cell should always have a fuse or polyswitch mounted directly on its case. That protects against frayed wiring starting a fire.

author: Circlotron
author_rank: Super Contributor
timestamp: December 03, 2018, 10:40:38 am
content: Quote from: tautech on November 26, 2018, 09:11:35 amThat's interesting. For sure, cycle it up and down a few times and see if things get better or worse.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 03, 2018, 12:15:50 pm
content: 50% is better than no battery, so it worked somehow.Now, it would be interesting to see the self-discharge rate. Charge the battery and leave it disconnected for a week, or so, then discharge it and compare how many Ah are still there after a week, or a month.For the next battery, it would also be interesting to try a normal charge first, and see if the battery can store any charge at all, and if it can store some charge, to measure the capacity in Ah. Then, to try the reverse charge rejuvenation, and see if there is any increase in how many Ah the rejuvenated battery can store.

author: tautech
author_rank: Super Contributor
timestamp: December 03, 2018, 05:23:13 pm
content: Quote from: Circlotron on December 03, 2018, 01:44:32 amOh, and all this talk about charging with a series diode.....that's for pussies !Nothing like the risk of blowing something up to keep your mind on the job.Quote from: RoGeorge on December 03, 2018, 12:15:50 pmWe're on the same wavelength.....shame it's coming into summer and oh so many jobs are piling up.QuoteOh you can be sure I'll be keeping my eyes out for furthervictimsbatteries especially any neglected and near new where IMO this rejuvenation method offers the best return for time invested.

author: TerraHertz
author_rank: Super Contributor
timestamp: December 05, 2018, 01:17:43 pm
content: cdev, here's some pics of what the insides of dead SLAs look like:http://everist.org/NobLog/20180430_lead_acid_ruin.htmWhat most people don't realize, is that in addition to sulfation of the plates (which forms a barrier to charge flow), there's another more serious effect, which is not reversible.The current-carrying matrix of solid lead mesh within the plates, becomes embrittled and develops cracks. Even the thick lead conductors up near the battery top can crack right through. When you find a battery that is completely open circuit, or won't take more than a few mA of charge current, this is what's happened. Nothing you can do is going to repair those cracks.I had a SLA from a big UPS, that seemed fairly OK. It had been left idle for a few years, but had only gone down to about 10V. Moving it, I put it down on the concrete floor. Then measured it again. Gone completely open circuit. The slight jolt had fractured an embrittled primary conductor path.

author: tautech
author_rank: Super Contributor
timestamp: December 12, 2018, 07:34:40 am
content: Tiny update on the 20Ahr SLA recovered and documented in reply #14.After some unsuccessful attempts to start the jetski it came in and even with a jumper battery paralleled for additional grunt, it's still holding ~12.3V after a week sitting idle. It's been freshened charged a couple of times and although hasn't got the grunt of a sound battery it's proved the Circlotron SLA battery recovery method is certainly of some benefit.Just popped it onto the same charger that was used for the recovery and @ 14V it drew 5A momentarily before quickly settling to 2.25A and now only a few minutes later to 200mA and still falling.OC voltage is certainly a bit low and this battery will get some desulphator treatment that in the past has proven to lift battery open circuit voltages.I'll come back to document those results when done and share some desulphator waveforms and the circuit.

author: CJay
author_rank: Super Contributor
timestamp: December 12, 2018, 09:30:59 am
content: Quote from: tautech on December 12, 2018, 07:34:40 amI'm intending to give it a go with some batteries over the Christmas break.I'm beginning to regret letting go of the 480AHr 2V cells they removed from our old phone system now but 37Kg a cell is a bit much to transport

author: tautech
author_rank: Super Contributor
timestamp: January 08, 2019, 09:40:16 pm
content: Status update on SLA recovered in reply #143 weeks idle = 12.0V (lower than satisfactory but OK for further attempts at improvements)Freshening charge applied......13.8V.

author: Circlotron
author_rank: Super Contributor
timestamp: January 08, 2019, 11:35:34 pm
content: ^^ Watching with interest.

author: m3vuv
author_rank: Super Contributor
timestamp: January 09, 2019, 05:14:24 am
content: looks to me like a pointless exercise to me tbh,just my thoughts.

author: Armadillo
author_rank: Super Contributor
timestamp: January 09, 2019, 07:39:43 am
content: It's easy to get confused....example lack of charge AH, sulfatant and internal leak.The first thing to do is to find out if the battery had internal leak, example it will hold the charge with enough decency or not.Reliability of start up is important to me, no point keeping something that when you most want it, it's not delivering.Dumpster it goes without a pain.

author: Armadillo
author_rank: Super Contributor
timestamp: January 09, 2019, 08:00:40 am
content: This subject on this old Rejuvenating will NEVER End.Sooner or Later, there will be someone bitten by the Dracula and the subject resurface again and again and again.......cause there are too many of them........Not Dracula, dumpster lead acid batteries around.These days, they seems to last for only a year, and the whole of the motorist industries dumps it, non stop every each year, about.

author: Armadillo
author_rank: Super Contributor
timestamp: January 09, 2019, 09:46:01 am
content: VRLA[AGM, Gel] , at 90F = Half Life but in reality 1 ~ 2 years.It's burden to maintain and time waster, I prefer flooded cells, rock solid.

author: tautech
author_rank: Super Contributor
timestamp: January 09, 2019, 05:16:57 pm
content: Quote from: m3vuv on January 09, 2019, 05:14:24 amQuote from: Armadillo on January 09, 2019, 07:39:43 amQuote from: Armadillo on January 09, 2019, 08:00:40 amQuote from: Armadillo on January 09, 2019, 09:46:01 amBest you both take some time to carefully read this entire threadandunderstand it !Heaven knows, you might just learn something, I know I didandproved it !Still more work to do on the 20AHr AGM.....with a desulphator, that in the past has lifted OC voltages even though the power that drove it was supplied from the battery it operated on. Yes, scary stuff !Do come back when you have somethingusefulto contribute.

author: Armadillo
author_rank: Super Contributor
timestamp: January 09, 2019, 06:12:15 pm
content: Please don't because of Thirteen Thousands+ you bring people merry go around, or you have a commanding say and do not accept criticism.I advice interested members to firstly check it is not internally leaked, other than sulfate or lack of AH before they even waste their time.Whether I contributed, is not for you to judge.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 09, 2019, 08:35:47 pm
content: ...What?Tim

author: floobydust
author_rank: Super Contributor
timestamp: January 09, 2019, 09:33:47 pm
content: Quote from: T3sl4co1l on January 09, 2019, 08:35:47 pmLately, the forum seems to have an effect on people's neurological processes.I checked with my bookie for odds on this battery getting rejuvenated. Finding water on Mars was 22/1 years ago.This battery down to 12.0V... so he gave me 100/1

author: Armadillo
author_rank: Super Contributor
timestamp: January 09, 2019, 10:20:49 pm
content: I read.After so much long hoo-ha, what appeared to be merely battery re-charging process as can be found in manufacturer datasheet and added with a bit of self-named merry go around here and there, doesn’t impress me.The tests are flawed with too much hypes and personal over-characterisation. It lacks international references. It can be seen in #14, that the battery exhibited 6 ohms load on initial discharging, which means it is NOT THE RIGHT CANDIDATE. Which means, this long hoo-ha PROOF NOTHING.For example [See pic], Manufacturer says for over discharged battery, to set current limit at 25V charge for 5 minutes for batt to recover after which they classified as “no good’. This should be the criteria for the right candidate to be chosen with Proper Qualification and Acceptable Undeniable reference made.Furthermore, there must a Proper Referenced Qualification of the “Recovered Battery”. For this [See pic], the battery should hold the voltage above the pass threshold after 2 hours. Alternatively, this can be used as a Selection Candidate for the De-Sulphate Process.Whether is 12K posting or 13K or 100K combined? The worse is disrespecting others and refusing to accept technical criticism.100 shares and 50 goes to Susan, doesn’t impress me. Please bear that in mind.

author: Armadillo
author_rank: Super Contributor
timestamp: January 10, 2019, 07:36:43 am
content: Quote from: floobydust on January 09, 2019, 09:33:47 pmHahahahahahahaThat's a good one.If he can "rejuvenate" a "right candidate" to less than 1/100, otherwise is a WASTE OF TIME pulling batt from the Jet-Ski in and out.Hahahahahahahaa

author: floobydust
author_rank: Super Contributor
timestamp: January 10, 2019, 09:30:16 pm
content: There is a lot of research on sulphation using scanning electron microscopy to look at the crystals.It appears the sulphate crystals are always forming on the plates. The size and effect of them always increasing. This isthe reasonlead-acid batteries are only good to say 500 cycles, have a limited life. It's the main aging mechanism.If you leave a battery discharged for 1 day compared to say 100 days, the crystals kept growing in size and sulphate is an insulator- a non-conducting salt, insoluble and filling the lead plate's pores- so you can't get rid of them really.We don't know how long OP's battery was sitting there dead.

author: tautech
author_rank: Super Contributor
timestamp: January 10, 2019, 09:44:59 pm
content: Quote from: floobydust on January 10, 2019, 09:30:16 pmYes but sulphation is part of the battery chemistry, it doesn't work without it.What is more important WRT sulphation is the type, some form very difficult to break bonds with the plates whereas others are migrated back into the electrolyte with ordinary charging or a gassing charge.Still others can be partially addressed with high energy electrical pulse desulphation.Battery construction determines what methods can be used to address sulphation.

author: BradC
author_rank: Super Contributor
timestamp: January 11, 2019, 04:17:18 am
content: Quote from: floobydust on January 10, 2019, 09:30:16 pmNo it's not. It is however a significant contributor if the batteries are undercharged. You can effectively manage sulfation during the operational life by managing the charge profile, but the side effect of that is corrosion of the plates.So an under-charged battery dies by sulfation. An overcharged battery dies by plate corrosion. Of course a battery that is kept exactly on spec (cool and with a temperature compensated charge voltage) will last longest, but ultimately barring a catastrophic failure it'll be a balance of plate corrosion and sulfation that drops its capacity past the threshold of usefulness.Example, the Vision 55AH SLAs I have here are now 16 years old. They have a design life of 10 years (which is defined by having greater than 80% of their original capacity remaining). When I got them 2 years ago they all measured out (at their C/10 rate) above or on spec, but they had been *very* well looked after. After 2 years in service I'm just about due to cycle them and see how they are fairing.

author: floobydust
author_rank: Super Contributor
timestamp: January 11, 2019, 07:17:38 am
content: You can do 500 cycles over several months or do the 500 cycles over many years. I think the +ve plate corrosion is a slower aging mechanism in SLA, flooded PbCa grids seem to corrode quickly.There are probably a hundred lead-acid battery failure mechanisms. Every paper I read has a different theory.In practice I find an overcharged SLA dies due to loss of water, and really old SLA fail due to plate corrosion. In constant float-use like a UPS, 59% plate corrosion and 33% dry out = 92% of the reason for failure.As far as sulphation, which I think OP is up against, it was a Reseachgate paper behind a paywall with scanning electron microscopy (SEM) showing the sulphate crystal growth progress and get larger with every charge/discharge cycle. They've been adding tin and graphene to hinder that, to get more than 500 cycle life.OP's only remedy left might be a pulse desulfator. But these fall under the category of voodoo and hope. I built the cheesy 555 timer version and it did nothing. Lots of threads about it, one poster did an open source very high current pulser that seems to work.https://www.eevblog.com/forum/projects/guess-what-will-happen-battery-desulfation-experiment/25/https://www.eevblog.com/forum/oshw/desulfate-regenerate-lead-acid-batts-a-new-diy-guide-overnight/https://hackaday.io/project/25741-desulfator-engine-re-climate-change-mitigationI'm surprised your Vision batteries have lasted so long, that is remarkable. But how many cycles they have, their temperature etc. is also surely a factor.I see many people now measuring battery ESR to determine health. It might be worth a try on gel-cells.

author: CJay
author_rank: Super Contributor
timestamp: January 11, 2019, 11:28:37 am
content: Quote from: floobydust on January 11, 2019, 07:17:38 amESR has been a 'thing' for determining battery health for some time, it works on gel cells too.I was selling testers that used the ESR principle ~20 years ago, alongside load testers and slightly more complex units like the SPX ARBST (which was ancient at the time) for the nay sayers who didn't believe a battery could be effectively tested by something that looks like a cheap multimeter.The results were more accurate from the ESR test but you needed to understand capacity, CCA rating, temperature effects etc.The load testers were trivial, connect it up, watch the needle, if it goes into the green bit the battery is good, if it doesn't, sales opportunity!!

author: tautech
author_rank: Super Contributor
timestamp: January 11, 2019, 12:07:57 pm
content: Quote from: CJay on January 11, 2019, 11:28:37 amGenerally from damage resulting from a carbon pile tester.Sir, your battery is sick.Yes I know, you just made it way.

author: CJay
author_rank: Super Contributor
timestamp: January 11, 2019, 01:18:28 pm
content: Quote from: tautech on January 11, 2019, 12:07:57 pmGenerally from damage resulting from a carbon pile tester.Sir, your battery is sick.Yes I know, you just made it way.Indeed, fortunately we didn't sell the carbon pile garbage but they were still in use in a lot of workshops, scary things with sparks and destroyed batteries and battery terminals, the ARBST was gentler but...

author: tautech
author_rank: Super Contributor
timestamp: June 28, 2019, 08:59:56 am
content: Well I must be a tiger for punishment as a couple of big chunky 12V Optima Deep cycle yellow tops have found their way to me.They're flat, really flat, each only a volt OC !It's only that I hold spiral wound cell Optima batteries in high regard that I'm willing to give these a fresh chance at further usefulness.These:https://www.optimabatteries.com/en-us/yellowtop-deep-cycle-battery/d31aCirclotron, are they worth the effort or am I?I do have some new tools.....a shiny new Siglent SDL1020X-E 20A electronic load that I can set all sorts of fancy for nancy loads and discharge cutouts.

author: Gyro
author_rank: Super Contributor
timestamp: June 28, 2019, 09:25:14 am
content: Quote from: tautech on June 28, 2019, 08:59:56 amThose look a bit of a bugger to clamp down, they certainly wouldn't work with the 'bottom skirt clamps in my car.Having said that, I still have a bunch of Gates Cyclon wound cylindrical cells that I rescued from the bin at work where the alarm company had dumped them, nearly 30 years ago! Despite severe neglect since, they are still going strong.Give them a nice long float charge at 13.8V.

author: tautech
author_rank: Super Contributor
timestamp: June 28, 2019, 09:34:16 am
content: Quote from: Gyro on June 28, 2019, 09:25:14 amThose Cyclon were sealed but flooded IIRC weren't they ?These Optima's were once solar and wind charged for a CB radio relay station that's fallen into disuse and sat neglected for a while.

author: Circlotron
author_rank: Super Contributor
timestamp: June 28, 2019, 11:22:56 am
content: Quote from: tautech on June 28, 2019, 08:59:56 amDefinitely worth a try! Those batteries are too good to just ignore.Did that other battery you worked on stay somewhat good?

author: Gyro
author_rank: Super Contributor
timestamp: June 28, 2019, 11:32:07 am
content: Quote from: tautech on June 28, 2019, 09:34:16 amNot sure about any excess electrolyte, I don't think so. They were (are) tightly wound AGM. The hidden resealable pressure vent doesn't vent until 50psi, that probably accounts for them holding on to their electrolyte.https://www.enersys.com/EMEA/CYCLON_Batteries.aspx?langType=1033

author: tautech
author_rank: Super Contributor
timestamp: June 28, 2019, 11:36:24 pm
content: Quote from: Circlotron on June 28, 2019, 11:22:56 amMy thoughts exactly.QuoteNah not so good.It's always struggled to hold charge/voltage and I've get to attempt to desulphate it but as winter kicks in I'll have more time to get back to it but I don't hold out too much hope for it.Still the process of attempting to rejuvenate it was well worth the learning experience and I thank you for the guidance offered while doing so.I didn't mention the big gell cell I scored along with the Optima's as it was holding some 12V after who knows long neglect and that one was first on the charger and seems fine as it's charge has fallen away to low current overnight but still needs some load tests to confirm whether it's any good or not.Todays job is to make some decent leads for my SDL E-load, do tests on this bad boy ^ and then properly flatten the Optima's in readiness for their reverse charge.

author: james_s
author_rank: Super Contributor
timestamp: June 28, 2019, 11:42:19 pm
content: Lead acid batteries are really a mixed bag. I've had some that failed within a couple years that I had no success in bringing back. I've had others amaze me, one car battery I dealt with was 14 years old, I managed to bring it back after it had sat for around 6 years and was at 0V, took a full charge which amazed me. I worked on the car some, got it running then it sat for another 5 years while my dad looked for the paperwork. Battery was again completely flat, 0V, but to my amazement it again took a full charge. It was in good shape too, in the process of waking the old car from its long slumber I cranked the engine intermittently for 2-3 minutes before it fired up and it was still cranking at a good rate when it started. I've wonder if it largely comes down to purity of the materials.

author: tautech
author_rank: Super Contributor
timestamp: July 01, 2019, 01:44:01 am
content: Quote from: tautech on June 28, 2019, 08:59:56 amIt's NOT true, I actually have a sickness...............batteries, the bigger the better !Came home with 6 of these bad boys that need some work...........but as they're made in OZ the jury is still out on that.Quick check reveals ~1V in each cell.Nice spot for them close to a powerpoint for charging and testing.Still looking for info that exactly matches the model # but the pdf below is probably close enough.

author: LapTop006
author_rank: Unknown
timestamp: July 01, 2019, 01:13:44 pm
content: Quote from: tautech on July 01, 2019, 01:44:01 amWow, haven't seen the BP Solar name in years. They were were common ~25 years ago in RAPS systems, but by the early 2000s were getting rare, at least in Australia. I just looked it up and the brand lasteduntil 2011/

author: rsjsouza
author_rank: Super Contributor
timestamp: July 01, 2019, 03:46:23 pm
content: I am going through a similar self-punishment process with a Yuasa 12V/7Ah purchased new in 2016 but by negligence (my own) I let it go down to 3.7V. I also found a Amptek 6V/4Ah that seems much more promising - it had 6.2V total but a very high internal resistance.I just found out this thread, thus I didn't try Circlotron method just yet. To me I have been cycling these batteries with a voltage charge of 2.4V/cell and the last charging cycle was throughout the weekend: 48h straight.The Amptek seems to be holding very well, with 2.19V/cell at the moment. I have been discharging this battery using a EBD-Mini electronic load I got from Franky many years ago. The past discharge runs showed is as being pretty weak: 59mAh when discharged from the full capacity to 1.83V/cell (5.5V) at 0.1A.The Yuasa is about 2.0V/cell after this weekend's 48h charge cycle, thus it probably needs a bit more "shaking".For me this is just an interesting exercise. I am pretty sure that, if none of this works out, I won't bebut instead being thankful of learning something interesting. At the same time I have been exercising the logging features of my E36312A and both my U1273A and U1282A.

author: CJay
author_rank: Super Contributor
timestamp: July 02, 2019, 09:07:06 am
content: I've just revived a pair of 75AH Lucas SLAs from a mobility scooter, both well under a volt at the terminals after being sat for at least four years (last time my MIL used the scooter), initially they didn't take enough current to register on the analogue meter on my PSU, after a good few hours they began to take current, rising to 300mA, enough to persuade my 'smart' charger that it needed to provide current to them.After six days they were holding a good charge and performed under a simple load test so I refitted them to the scooter and drove it.For over an hour before I got bored.It's now been a little over six weeks since I refitted them, they've had four charge cycles and they seem to be working just fine.Well worth the effort give that they are approximately £160 each.

author: rsjsouza
author_rank: Super Contributor
timestamp: July 17, 2019, 09:39:40 pm
content: I didn't yet try Circlotron's method on the 6-cell Yuasa, given the charge/discharge cycles on it are yielding an ever growing ramp that is currently at 2Ah.The 3-cell Amptek was much less promising: it was peaking 150mAh (120mAh was the norm). After Circlotron's method (48h at negative 6.6V, then 48h at positive 6.6V, both at 100mA) I just finished the test on the electronic load and got almost 480mAh - still at 10% of the top capacity.I'll try the rejuvenation method once again on the Amptek, but I think it will be binned if things don't improve.At any rate, it is an interesting exercise.

author: tautech
author_rank: Super Contributor
timestamp: July 23, 2019, 03:49:24 am
content: Quote from: tautech on June 28, 2019, 11:36:24 pm3 weeks continual charging later....this gel cell reached full charge as in that another linear smart charger reported it as fully charged at 14.26V. After a few hours rest 13.12V.Some load tests next to see how it behaves.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 14, 2020, 04:49:29 pm
content: Found yesterday a discarded 9Ah/12V UPS battery. It was written on it "Maintenance-free Sealed Lead-acid Battery", which remembered me about this thread and Circlotron's reverse charging recovery method:https://www.eevblog.com/forum/repair/attempt-rejuvenating-old-gel-cell-lead-acid-batteries-with-a-bench-supply/msg1985024/#msg1985024, so I took it home out of curiosity to test the reversed charging recovery.The battery measured 3.5V with no load, and took no charging current when trying to charge it with 14.4V and the correct polarity. Since it was a lead-acid battery and not a gel one, I first assumed it was dried out. Cracked open the top cover, removed the rubber plugs and fill each element with de-ionized water until the water was was about 3 mm above the plates.After filling it with water I was expecting to take at least a few mA in normal charging mode, but nope. Still nothing, so I connected the battery with reversed polarity (- of the battery to the + of the charger), with the power source set at 14.4V/180mA max. The current indicated by the power supply was about 30mA at first, and in a few minutes reached the 180mA set limitTo my surprise, after a few minutes of reversed charging, the voltage started to jump/fluctuate (about a few times a second, or so, between jumps), also it was some very, very slow gassing (I left the rubber plugs opened), so I startlogging the voltage at each minute.Strangely, the time between voltage jumps was random, but the voltage was about 1.2V or so.Today I give it another try, this time using good wires instead of the very cheap Chinese banana/alligators wires from yesterday. Now there are no more voltage jumps, and I'm curios if this is because the plates had time to soak over night, or because of the good wires.TL;DRAnybody remember seeing voltagevariationsjumping approx. 1.2V up and down during reverse charging?

author: tautech
author_rank: Super Contributor
timestamp: January 14, 2020, 07:34:20 pm
content: If you are using CC PSU mode yes the voltage will drop as the battery starts accepting charge....reverse or forward charge.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 14, 2020, 08:48:22 pm
content: Sloppy English from my side, sorry.Not voltagevariations, I was asking about the voltagejumpsof about 1.2V back and forth, like the ones seen in the lower left corner of the chart. (The smooth voltage increase up to positive voltage is what happened after disconnecting the battery)

author: RoGeorge
author_rank: Super Contributor
timestamp: January 15, 2020, 10:30:53 pm
content: After more than 24 hours left in reversed polarity charging, the voltage still jumps back and forth about 1.2V, while the current is stable at 180mA, as set. Temperature was constant all the time, the elements doesn't heat, they are between 1.5 ... 2.5 Celsius more than the room temperature.Looking at the chart, it looks like an element (or maybe two of them) sometimes are short circuited, sometimes not, and it does that by themselves.Anybody noticed something similar during charging a Lead-acid with reversed voltage polarity?Any ideas why those voltage jumps are happening?

author: RoGeorge
author_rank: Super Contributor
timestamp: January 16, 2020, 03:37:19 pm
content: Got bored after about 30 hours of reversed polarity charge, the voltage kept jumping up and down in steps of 1 or 2 cells (1.2 or 2.4V).Switched the plugs to charge with normal polarity, 15V/180mA limited (2% of C), through a protection diode. Over nigh the voltage was stable at about 7...9V, still jumping but not so often. Will add a chart for that period, too.Then, the 180mA current limiting was removed, and the battery started to draw about 2A at first, and after a few hours, about 1.5A.Sometimes the battery is fizzling and popping. Looking at the voltage with an oscilloscope, there are periods with cleaner voltage, and sometimes strong noises with an increasing in amplitude, sometimes up to 2Vpp.The moments when oscillations suddenly stop seems to be correlated with the popping while the increasing of amplitude is correlated with the fizzling. Strange that the audible fizzling is almost constant in amplitude, while the oscilloscope always show an increasing amplitude.Just for the fun of it, the random and increasingly oscillations, and another cleaner trace for the periods when the battery doesn't fizz and pop:

author: mikerj
author_rank: Super Contributor
timestamp: January 16, 2020, 04:57:40 pm
content: I wasted many hours in my youth trying to rejuvenate dead lead acid batteries using various charging regimes and chemical methods (Epsom salts iirc) and the results were never worthwhile. Some of them would accept a charge, but they invariably had low capacity and significantly raised impedance so they weren't very useful.I managed to hurt a virtually new car battery (VARTA) by inadvertently leaving the headlights on for about 10 hours, and whilst it recovered sufficiently to start the car just that one event had clearly dented it's performance as the engine never turned over quite as enthusiastically.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 16, 2020, 05:35:55 pm
content: I don't hope to recover the battery and don't even need it, just being curios to log the data and see what happens.For this particular battery seems like 2-3 elements have an internal short-circuit, probably some dendrites between plates, since the voltage stays at about 9.4V when disconnected from the charger.I would like to probe the voltage for each element, but the connections between elements are not visible. Couldn't find any pics that shows where are the internal bridges between elements. I want to drill some small holes right above the internal bridges, so I could measure each element's voltage.Anybody have a picture of the inside of a typical 7-8Ah UPS sealed lead-acid battery, so to locate where exactly are the interconnections?

author: tautech
author_rank: Super Contributor
timestamp: January 16, 2020, 06:59:27 pm
content: Quote from: RoGeorge on January 16, 2020, 05:35:55 pmThat certainly doesn't look good and I would chop the top off it and use it for a build study. There might be some good cells in it but some of them are certainly pooped !Meanwhile a 22AH 12V SLA has found its way onto my bench and it measured 0.6V after an unknown period of inactivity. It's out of a portable Pelican floodlight system. Refused to accept charge from the system charger.Siglent SPD1305X lab PSU selected for attempted recovery.Reverse charge started some 15 hrs ago @ 2% CC.Currently drawing ~500mA......~30mA fluctuations reported by LCD readout.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 17, 2020, 01:08:58 pm
content: Best luck with your battery! Mine certainly has at least 3 bad elements.Charged it yesterday, and over night it dropped from 11V to only 7V. At a closer look, some rocky gray pebbles about the size of a corn or rice grains can be seen on top of the elements.Took one small pebble out with a pair of tweezers made out of 2 toothpicks, and try to measure if it is conductive or not. It was very funny. Since the pebble was soaked with sulfuric acid and certainly had some Pb in it, too, together with the tip of the probes it was making a tiny battery that completely bamboozled the ohmmeter indications.On the mV range, no matter where the little pebble was poked with the probes it was showing about -100..-200mV, always negative no matter how the probes were switched.Meanwhile, found out from some dismantling videos where under the lid those interconnecting bridges should be located :Also found a paper about the main failure modes of lead-acid batteries: Catherino, H. A., Feres, F. F., & Trinidad, F. (2004). Sulfation in lead–acid batteries. Journal of Power Sources, 129(1), 113–120. doi:10.1016/j.jpowsour.2003.11.003https://sci-hub.tw/10.1016/j.jpowsour.2003.11.003Sulfation is only one of the many other ways of failure, and doesn't seem to be the most frequent one, according to the paper:Quote from: doi:10.1016/j.jpowsour.2003.11.003Will probably open the battery out of the curiosity to see how bad it is looking on the inside, not sure when, since it's cold outside and indoors I don't want the mess of a dismantled SLA battery.

author: tautech
author_rank: Super Contributor
timestamp: January 18, 2020, 07:07:58 am
content: Quote from: tautech on January 16, 2020, 06:59:27 pmQuote from: RoGeorge on January 17, 2020, 01:08:58 pmThanks.Progress report~48hrs reverse charge in CC mode, the PSU was displaying ~12.5V still in CC mode with a target of 14.5VReverse mode charge terminated and battery rested some 10 minutes where it measured ~9.5V reverse polarity.Warm 25C day here today and battery temp was just warm to the back of the hand.Application of a 30W 12V incandescent bulb load caused the reverse voltage to fall away completely and wouldn't light the bulb. Yet it bounces back to ~9V. Didn't measure current taken by bulb load.Forward charge commenced.Target 14.5V @ 400mA in CC mode.PSU reports 0.0V @ 400mAfor a few minutes until the forward polarity becomes established then the voltage starts to count up and has already reached ~8.5V in a few short minutes.Due to the residual heat from the reverse charge the charge rate in CC mode will be halved to 200mA to ensure the battery stays at acceptable temps.Fingers crossed for this one !

author: Circlotron
author_rank: Super Contributor
timestamp: January 18, 2020, 12:04:34 pm
content: ^^ I don't think I'll sleep tonight!

author: tautech
author_rank: Super Contributor
timestamp: January 19, 2020, 06:33:55 am
content: Quote from: tautech on January 18, 2020, 07:07:58 amQuote from: Circlotron on January 18, 2020, 12:04:34 pm~24hrs with forward charge of which ~7hrs overnight was @ 200mA.Charger displaying ~12.57V @ 400mA and the rate of voltage increase has slowed somewhat indicating good charge absorption. Battery barely warm to the touch despite a hotter day here than yesterday.A few minutes rest and it measures 11.8V.14.5V target 400mA CC forward charge resumed........

author: RoGeorge
author_rank: Super Contributor
timestamp: January 19, 2020, 08:12:50 am
content: Quote from: tautech on January 19, 2020, 06:33:55 amLooks like one element is bad.

author: tautech
author_rank: Super Contributor
timestamp: January 19, 2020, 08:36:02 am
content: Quote from: RoGeorge on January 19, 2020, 08:12:50 amI don't draw that conclusion just yet as the recovery is a while from finished, maybe even 2 full days yet.CC voltage was 12.57 ~2hrs ago and it's still slowly rising @ the 400mA CC charge. Currently (excuse pun) 12.62V.The rising voltage indicates a rising SOC and while I might have the target voltage a tad high @14.5V when the battery gets to ~14V the current draw should reduce indicating a high SOC. If not we start looking for the voltage point where the current reduces which should indicate if all cells are behaving themselves.Ideally we'd like to see a resting static voltage at a high SOC @ 2.2V * 6 =~13.2V. Anything above 12.8 I'm happy but load tests are the proof of any real success.Others I have tried but older worn batteries have dropped their guts after a couple of days rest to measure sub 10V and they're not worth wasting more time on.So for now we just wait and watch.......

author: Circlotron
author_rank: Super Contributor
timestamp: January 19, 2020, 12:37:46 pm
content: Quote from: tautech on January 19, 2020, 08:36:02 amYep, I never had particularly good results trying to revive a worn out battery. Mine were brand new unused but had sat around for 5 years or so and had a terminal voltage of about 2V.

author: tautech
author_rank: Super Contributor
timestamp: January 20, 2020, 12:44:59 am
content: Quote from: tautech on January 19, 2020, 06:33:55 amYeee haaaa !We might finally have a recovery !After some 40 hrs of forward charge with 14.5V target the target voltage is now met and the charge rate has dropped to 220mA from a CC 400mA setting.Battery cold.After a short rest it measures 12.5V.....a bit low for my liking.Back on charge.@CirclotronI'll try some discharge/charge cycles next, what minimum discharge voltage do you recommend ?I do have a 30A programmable load........

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 20, 2020, 01:38:13 am
content: How about zapping it with some high current pulses (say >10A charging, or >50A discharging)? May be able to clear the short (fallen material/dendrites?), not that it'll last of course.Tim

author: tautech
author_rank: Super Contributor
timestamp: January 20, 2020, 02:32:03 am
content: Quote from: T3sl4co1l on January 20, 2020, 01:38:13 amI do have a old DIY desulfator that emits 1KHz 60V @ 7A pulses and plan to give it an overnight session at some point. It has worked pretty well in the past improving static (resting) voltage levels but it's only designed to address plate sulfation that isn't moved in normal charging.

author: Circlotron
author_rank: Super Contributor
timestamp: January 20, 2020, 12:03:04 pm
content: Quote from: tautech on January 20, 2020, 12:44:59 amMmm... I'd say no lower than 11 volts and not more than 0.2C discharge rate. Just take it easy for the first few cycles at least. Just my gut feeling, not scientific.

author: tautech
author_rank: Super Contributor
timestamp: January 21, 2020, 08:40:10 am
content: Quote from: Circlotron on January 20, 2020, 12:03:04 pmIt's not as good as I might have wished and after 24rs standing 12.0V !Some gentle cycles and some desulphating are the next order of business.......1 minute later.......Nah, it's dead Jim !Won't even withstand a 30W load !

author: RoGeorge
author_rank: Super Contributor
timestamp: January 21, 2020, 05:41:12 pm
content: Today, at about 5 days of rest after charging, the total voltage was only 5.77V, so just out of curiosity to see how each element is doing, but without dismantling the whole battery:- drilled a 1mm thin hole above each of the internal bridges between elements (watch the video above to identify bridges location, they are on the external sides, at about 1/8 of the total battery width)- measured the voltage and the short-circuit current of each elementCode:Element Open Short# Voltage Current(+ to -) (V) (A)1 0.8828 0.2952 1.1397 1.7113 1.8817 2.7554 1.8736 7.3385 0.0052 0.0006 0.0017 0.000Total 5.7847The 4thelement seems strong, it can deliver more than 7A of current when shorted, and since the wires were pretty long, most probably it can supply much more than 7 Amps.The surprise was that none of them has the expected 2.4V or so (for a charged element), not even the strongest one, which led to the conclusion that the self-discharge rate was very high.Would have been nice to poke the measuring holes earlier, fit a self-driving screw in each of the 5 internal bridges, then log the voltage on each of the six elements over a few days, during charging and self-discharging.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 21, 2020, 07:34:58 pm
content: All of this work supports the recommendation of several people in this thread. That it is seldom, if ever, worth trying to rejuvenate these things. It is a lot of effort. It only "works" occasionally. And when it does work the result is a substandard battery.The best way to get some use out of these things is to send them to the lead recycling facility.

author: Circlotron
author_rank: Super Contributor
timestamp: January 21, 2020, 09:04:21 pm
content: You must have never felt the satisfaction of bringing a battery back to life. It’s like fixing an old piece of equipment that everyone else says ought to be scrapped. But, to each his own.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 22, 2020, 02:29:45 am
content: I have. I have restored both lead and nicad chemistry batteries. And dis-assembled LiPos to get good cells out of the packs and build into "good" packs. But each time the smile was wiped off my face in a few days or weeks when the "restored" battery failed again. In a few cases I even revived those failures.If you have any access to a supply chain to get new batteries and if restoring old batteries is not your hobby nirvana do it often enough to learn the limitations and then don't do it again. But if restoring these batteries is what floats your boat, go for it. You will have lots of opportunity for the joy of trying and occasionally succeeding.

author: BradC
author_rank: Super Contributor
timestamp: January 22, 2020, 07:56:26 am
content: Quote from: Circlotron on January 21, 2020, 09:04:21 pmI can honestly say I've never felt the satisfaction of bringing a battery back to life. I have "revived" batteries sufficiently to perform a severely underrated role (Like the 7.2AH SLA that holds ~1AH @10V and runs solar lights). But I've never got anything close to rated capacity or internal resistance.Splitting up packs of NiCD/NiMH/Li-ion and picking the eyes out to repair a pack, certainly. But again, at a reduced capacity of some sort.There are advantages to that sometimes. I have a 12V 17AH SLA here that I let my boys play with. It'll hold ~12V with a <30W load, so they light up leds, 21W car tail lights, run DC fans and all sorts of stuff, but it won't set fire to the carpet like the battery I had as a kid that ignited an aluminium bicycle spoke I shorted it out with. It saved me building some form of current limiter and they can play to their hearts content. It even holds > 10AH, but the voltage just collapses under load. Does the battery have any real world use? Not really. It's old and tired (like me).This is one of those topics that comes up every few years, and it always generates some enthusiastic participation, but in the end the result is universally the same unless you count "bringing back to life" as 1/10th of the original capacity, will self discharge in a week or two and has a high internal resistance.Lead acid is a pretty well understood chemistry and construction. There really are no magic bullets.Edit: Meant to add. Replacing the electrolyte in a flooded lead acid with pool acid (~30% hydrochloric) actually generates some neat potential with the downside of also generating non-insignificant proportions of Chlorine gas and HCl vapour. Still, I had to learn the hard way.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 25, 2020, 06:08:43 pm
content: Poking a cadaver might seem gross at first, yet valuable as a studyFrom the last check, the 3rd and the 4th elements appeared to be in reasonable shape, one was capable of about 3 Amps short-circuit current, the other, 7A. Both were way under the expected voltage, at only about 1.9V with no load.Yesterday they were refilled again with water, then plugged them to charge for about 24h at 0.5A. Not the best idea, because during charging the electrolyte overflowed a little. Should have replenished the water after charging them, not before. Paper towels helped to not make a mess out of this.Now, 24h later, elements 3 and 4 are about the same voltage, 2.0V each when left with no load, but when short-circuited the max current is still slightly different, 10A and 13A. The difference in max current is not so big now, maybe the previous 3A vs 7A was because they were not charged enough. Will keep charge them till tomorrow.However, until now more than 20Ah were poured in each element (the battery is only 9Ah), so by now they should be fully charged, yet the voltage is only 2.0V instead of the expected 2.4V of a fully charged element at room temperature.At this point I suspect there was so much sulfation that a big percentage of the initial H2SO4in the electrolyte was fixed in the PbSO4crystals, so now the electrolyte does not have enough H2SO4left, and that is why the open circuit voltage can not go bigger than 2V no matter how much those elements are charged.Should either add some sulfuric acid (which I don't have any), or maybe find a way to break the PbSO4crystals stored on the plate as sulfation, and make them dissolve in the existing electrolyte. Normal charging can not break large PbSO4crystals. Will see about that later.Even so, with only 2V, there should still be about the same energy stored as it would be stored by a 2.4V element, just that the max current will be lower. Didn't measured the C yet, so for now this is just speculation.Not sure for how long this screws in the pic will last, but if the location is just right, self driven screws on an initial 1mm drilled hole right above the interconnection bridges can make great terminals to temporarily access each element.

author: SeanB
author_rank: Super Contributor
timestamp: January 25, 2020, 06:37:15 pm
content: With NiCd cells I made a rejuvenator for cordless phone batteries, as I used a Panasonic cordless phone ( KXT 9080A, the version that was not type approved in many countries, because it had over 1W of RF output, unlike the 50-100mW of the others in the range, meaning it worked with a range of around 1km), and repacking the batteries every year or so because a cell was dendrited was annoying. It was simple, an old transformer that provided around 60VAC, and a single diode charging up a recycled capacitor, around 470uF 160V IIRC, that was discharged into a pair of nuts and bolts attached to the front panel at the right spacing to fit the battery contacts. A old industrial push button assembly to connect the capacitor to the terminals, and I had a quick and dirty dendrite remover tool.Worked well enough, in that a zapped pack would not have a dead cell any more after a zap or three, measuring after each pulse with a DMM to see the open circuit voltage go up by 1V or more. Zap, check and then charge overnight, then use my discharger, a small piece of galvanised steel angle with a 10R 10W aluminium cased resistor screwed to it, with a 6V grain of wheat bulb across it, and 2 stiff copper wires to fit the battery. Place across battery and leave till lamp is out, then charge, and if giving low voltage from phone, zap and charge again. Saved me from buying a lot of AA NiCd cells, as the most common types of tagged AA cells I could get were just too long to fit the packs.That cordless phone lasted well, the others all eventually were killed by people, so I had plenty of spare parts to keep mine running, while the others were replaced with what we jokingly called " Same Room" phones. expensive to repair though, back when you could actually get spare parts for equipment, and Matsushita actually had a repair centre worth the cost. Lots of main boards, front flaps and flex boards, because people smash things not theirs. I must have paid their tech his salary some months.

author: Gyro
author_rank: Super Contributor
timestamp: January 25, 2020, 06:43:45 pm
content: Quote from: RoGeorge on January 25, 2020, 06:08:43 pmSurely even 7A is nothing for short circuit current on a cell of that size of SLA, it ought to be about an order of magnitude higher. I remember accidentally making the jaws of a pair of snipe nose pliers glow red hot trying to discharge a remaining cell on a smaller faulty SLA than that (6.5AH iirc) before disposal.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 25, 2020, 06:58:22 pm
content: Quote from: SeanB on January 25, 2020, 06:37:15 pmI did something similar in the past, for 1.2V NiCd elements.Some of them were short-circuit internally by metallic dendrites that grow by themselves (self-grown metallic dendrites were observed growing inside vintage integrated circuits, too, not only inside batteries). A few seconds of a 12V lead-acid battery connected with thick wires directly at a 1.2V NiCd battery will burn any internal dendrites in the NiCd battery, and make it work again, but not for long. In a few days or weeks, the short circuit appeared again.

author: SeanB
author_rank: Super Contributor
timestamp: January 25, 2020, 07:30:42 pm
content: It worked well enough to get a month or so per zap, and I always had a spare battery pack on hand to swap out for it. Yes the dendrites always grow back, but for daily cycling it was worth it, as new cells would do the same in a few months anyway, as the Panasonic charge circuit was bound up in the microcontroller on the board, and simply did a sort of constant current charge while monitoring current to light a LED, and disabling the phone side when charging. No room to add anything inside, and a PITA to get to those boards inside, as they were well hidden by other boards soldered over them, along with all the soldered on paper and foil shields.

author: Gyro
author_rank: Super Contributor
timestamp: January 25, 2020, 08:12:07 pm
content: A good article on NiCd cell failure modes and recovery that I remember from Wireless World Magazine...https://www.americanradiohistory.com/UK/Wireless-World/80s/Wireless-World-1985-06.pdfP.S. Magazine page 60.

author: RoGeorge
author_rank: Super Contributor
timestamp: February 19, 2020, 02:23:00 pm
content: Just FYI, same SLA battery I was poking at in the previous page, now 1 month later.