EEVblog Electronics Community Forum

Electronics => Power/Renewable Energy/EV's => Topic started by: Fflint on December 02, 2021, 12:27:06 pm

Title: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 02, 2021, 12:27:06 pm
I recently became interested in reconditioning of old lead acid batteries. Reconditioning in context of lead acid batteries usually means desulphation of negative electrode.

There are lots of very similar articles online about how to desulphate those batteries. Half of them talk about using magnesium/sodium/cadmium/lithium(choose one) sulphate salts. The other half describe various circuits that send high frequency current pulses through the battery.

There are few scientific articles on the subject, but they tend to have very narrow focus.

For example one article looking into magnesium sulphate use found that 2% of it in the electrolyte lowers the negative electrode internal resistance and it has some other minor benefits. Unfortunately, they didn't make any comparison of capacity before and after. Then another article tested the pulsed desulphation and they too found benefits, but they didn't test battery capacity before and after, just the way it charged.

Finally, there is another article written at batteryvitamin.net that claims both methods manage to at the very best restore 10% of original capacity.

So the conclusion is? I have no idea.

So, having two old tractor batteries I decided to test the magnesium sulphate method. The tractor batteries are 6 volt, 165amp-hour units that used to work in series. When I bought the tractor 3 years ago it came with the batteries. By the newish looking stickers I estimated the batteries to be no more than 5 years old at time of purchase. Two years ago in winter, the batteries failed to start the tractor (in - 15C) unless charged for few hours. Then they failed to start it even in summer (+25C) so I bought a new set. The old set sat in an unheated shed for two years. Few days ago when I measured the voltage there was none - 0 volts. On both batteries. I dumped the old electrolyte to a bucket (there was 9L of it). And I made a solution of 2kg of magnesium sulphate (7*hydrate) in 9l of warm deionised water. I filled the batteries with that solution and I started to charge them using two lab PSUs.

Surprisingly they behave very differently despite the fact they were used very similarily.

 Battery no 1 upon charging with constant current of 0.5A went to 7.4V (this is equivalent to 14.9V if this was a 12v battery) and sits at 120mA and that voltage.

Battery no 2 behaves much better. I initially set the current limit to 1A. It reached the limit at 6.3V (12.6V equivalent). I kept it like this for 12h and the current dropped to 200mA. So I set the current limit to 2A and voltage to 7.3V. The battery has been taking 2A of current at 6.85V(13.7 equivalent) for last 12H.

24h have passed since I started charging them. Initially the plates looked light gray wth white sprinkled over. Now they look dark grey with reddish-black patches.

I have two more batteries to try to fix. They are in much better state. One is a diesel car battery 12V, 75AH.This allegedly has lost the majority of its capacity. Its voltage in storage is pretty good at 12.5V. The second is a backup power battery 12V 100Ah. This one allegedly is completely dead and fails to charge. Its storage voltage is 11.5V.

Is there anyone here with experience of attempting to restore old batteries like this? I would be very interested in hearing your positive and negative experiences. Am I wasting time trying to fix them? I was very skeptical regarding most of positive restoration claims I read before, but seeing how well one of those old tractor batteries charges I'm not so sure.

My plan for the older of two remaining batteries is to add enough magnesium sulphate to achieve 2% concentration and to try to charge.

I may try cobbling together a pulse desulphator for the remaining one.

Please don't reply just saying to buy a new one. I know I can do that, but I like fixing and restoring old things such as those batteries. If I'm successful restoring at least 50% capacity I'll use them for backup power. If my attempts fail I'll sell them for recycling.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: NiHaoMike on December 02, 2021, 01:38:50 pm
You can make an easy pulse desulfator out of a triac light dimmer (set to about halfway), a 5-10uF motor run cap, and a bridge rectifier. Triac light dimmers work by cutting the AC waveform, pass that through a cap and you get pulses, when you then rectify with the bridge rectifier.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 02, 2021, 01:56:09 pm
You can make an easy pulse desulfator out of a triac light dimmer (set to about halfway), a 5-10uF motor run cap, and a bridge rectifier. Triac light dimmers work by cutting the AC waveform, pass that through a cap and you get pulses, when you then rectify with the bridge rectifier.

Thanks. There are hundreds of circuits online too. I would probably use my signal generator with a power mosfet transistor as I don't have a dimmer. However, I'm more interested in if there is anyone with positive or negative experience of actually using those circuits, or chemical methods.

How much capacity can one reasonably expect to restore? Is it only 10%? If yes, there is no point. If it is ~50% it is very interesting.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: NiHaoMike on December 02, 2021, 02:24:37 pm
My experience is that it's far more effective at restoring a weak battery than trying to revive a totally dead one, and is more effective on conventional lead acid than sealed lead acid.

I used to have a Belkin UPS that charged the battery with brief high current pulses using some circuit in conjunction with the inverter transformer. The battery lasted about 5 years compared to 3 years for APC which used the same kind of battery but DC charging. Main downside is that the high current pulses cause interference with nearby analog audio equipment.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: rsjsouza on December 02, 2021, 03:16:20 pm
There are a few discussions around EEVBlog about the subject. One of them with some interesting results is at:
https://www.eevblog.com/forum/repair/attempt-rejuvenating-old-gel-cell-lead-acid-batteries-with-a-bench-supply/ (https://www.eevblog.com/forum/repair/attempt-rejuvenating-old-gel-cell-lead-acid-batteries-with-a-bench-supply/)
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: HighVoltage on December 02, 2021, 03:18:42 pm
This is how they recondition a battery in Pakistan, I believe

https://www.youtube.com/watch?v=l665eovBlEk (https://www.youtube.com/watch?v=l665eovBlEk)
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 02, 2021, 06:34:28 pm
Thanks for the link to the earlier thread.

This is how they recondition a battery in Pakistan, I believe

https://www.youtube.com/watch?v=l665eovBlEk (https://www.youtube.com/watch?v=l665eovBlEk)


Wow. That is more of a replacement rather than reconditioning. There is only a container left from the original battery. I love how he welded the plastic together without using any glue :-)

No doubt those plates he's using came from some factory in China. Other than not using gloves and respirators for handling lead all day every day and dumping old electrolyte on the ground there is nothing wrong with his method. It looked like he was "reconditioning" a 240AH 12v battery. Here in EU those batteries start at $250. I wonder how much he charges :-)
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 04, 2021, 12:30:48 am
A quick update.

It seems the magnesium sulphate treatment continues to help as the batteries are charged.

I shorted the tractor batteries today to test them. I used a very thick jumper lead and I measured the current with a clamp on meter. The better (tractor) battery produced about 100amps. The worse only 4! I kept them shorted for around 30s.then the cable was removed. In both batteries voltage recovered to around 6.2~6.3V then. Tomorrow I'll try cobbling together a pulsing circuit.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 06, 2021, 10:30:16 am
Another update. Both tractor batteries were on trickle chargers. The better one was taking few amps, the worse one around 1A (at 7.8V).

It seems both batteries are slowly improving. The better one managed to produce 400~380Amps when shorted. Worse one about 30A. That is a 4-fold increase after 2 days. If the trend continues the prognosis is good :-)

I haven't put together a pulse charger yet. I would like it to have at the very most 1uS on/off slope and few hundred amps. It seems without dedicated mosfet driver IC that is pretty difficult to achieve. So I've ordered some drivers and extra mosfets to play with.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 07, 2021, 03:04:47 pm
Well, the conclusion of the magnesium sulphate treatment is that it nicely removed surface sulphates, but it does nothing deep inside the pores. It makes plates look new however so makes for really nice before and after pictures. Those are however pointless without the increase in capacity.

I've built a pulse charger and I'll be using it in thd next stage of this "experiment".
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 07, 2021, 06:42:20 pm
Well, it seems not every battery can be saved. I was becoming a bit frustrated with the worse of the tractor batteries not responding to my repair attempts (I did manage to get 30 CCA once, but then it went back to 7~8 amps.

So I decided to open it up for an inspection(I was really gentle with opening) and this is what I found:
(https://i.ibb.co/s1J9n1m/20211207-192100.jpg) (https://ibb.co/4SgRzSm)

The color of plates is nice, at least magnesium sulphate desulphation did its job :-)

Wow, the busbar in the middle cell is cracked (how did that happen?). The left most cell has all of its positive plates disconnected. The other busbar in the middle cell looks seriously deformed. It is a miracle I managed to get 7~8 amps from it.

I have a couple other batteries to test. I sure hope they look better inside than this.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: rsjsouza on December 07, 2021, 08:54:30 pm
Wow, the busbar in the middle cell is cracked (how did that happen?). The left most cell has all of its positive plates disconnected. The other busbar in the middle cell looks seriously deformed. It is a miracle I managed to get 7~8 amps from it.

I have a couple other batteries to test. I sure hope they look better inside than this.
Indeed interesting; perhaps the heat from the high current combined with the weakened material of the busbar were enough to cause deformation and the crack.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: floobydust on December 08, 2021, 01:33:04 am
Corrosion is a high cause of failure, but that middle cell looks like somebody gave it a kick or maybe a hydrogen light up happened. A spark occuring in a cell can rarely do that.
I think measuring ESR would be worth trying, to tell you right off the bat the battery is damaged.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: james_s on December 08, 2021, 02:59:39 am
The lead seems to get brittle over time, I've taken apart SLA batteries on a few occasions and every one of them that I took apart pretty much crumbled to bits. I have experimented with reviving dead lead acid batteries a few times and I've found if they don't recover after sitting on a normal charger for a while they are pretty much shot. You might squeeze a bit more life out of one but not enough to be worth the effort.

That Pakistani battery rebuilding video is a crude but effective example of the only way to really truly revive them. They aren't just replacing the guts, they're taking apart the batteries, melting down the plates to reclaim the lead and then forming new plates and bus bars out of the reclaimed lead. In developed nations we do more or less the same process, in a far more controlled and industrial process. I saw a video about that somewhere a while back, they had a huge machine that all the old batteries got dumped into, it would grind them up and separate the plastic, lead and acid for re-processing into new raw materials.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: floobydust on December 08, 2021, 03:38:34 am
I did not see them recycling the lead, they seem to be using new pre-made plates obtained from somewhere  :-//
Large stationary deep-cycle batteries have tons of room at the bottom for the plate material to accumulate, lots of lead dust at the bottom. They seem to be constantly disintegrating.
If you think about it, how many metals don't mind being in acid for years...
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: vk6zgo on December 08, 2021, 05:39:46 am
The lead seems to get brittle over time, I've taken apart SLA batteries on a few occasions and every one of them that I took apart pretty much crumbled to bits. I have experimented with reviving dead lead acid batteries a few times and I've found if they don't recover after sitting on a normal charger for a while they are pretty much shot. You might squeeze a bit more life out of one but not enough to be worth the effort.

That Pakistani battery rebuilding video is a crude but effective example of the only way to really truly revive them. They aren't just replacing the guts, they're taking apart the batteries, melting down the plates to reclaim the lead and then forming new plates and bus bars out of the reclaimed lead. In developed nations we do more or less the same process, in a far more controlled and industrial process. I saw a video about that somewhere a while back, they had a huge machine that all the old batteries got dumped into, it would grind them up and separate the plastic, lead and acid for re-processing into new raw materials.

Pretty much how they rebuilt batteries in Australia for years.
The plastic (or in earlier years, "hard Rubber") case is the only part that really needs a large factory to make.

Obviously, in Oz, they did it in a proper workshop, not on the side of the road, but the technique would be basically similar.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: james_s on December 08, 2021, 06:12:52 am
I did not see them recycling the lead, they seem to be using new pre-made plates obtained from somewhere  :-//
Large stationary deep-cycle batteries have tons of room at the bottom for the plate material to accumulate, lots of lead dust at the bottom. They seem to be constantly disintegrating.
If you think about it, how many metals don't mind being in acid for years...

They probably process the lead somewhere else, they must use a machine to form it into sheets. It wouldn't make sense to just throw it away though, lead is valuable and easily recycled.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 09, 2021, 02:18:49 pm
I did not see them recycling the lead, they seem to be using new pre-made plates obtained from somewhere  :-//
Large stationary deep-cycle batteries have tons of room at the bottom for the plate material to accumulate, lots of lead dust at the bottom. They seem to be constantly disintegrating.
If you think about it, how many metals don't mind being in acid for years...


Perhaps I posted a wrong link. There are a couple of those videos made by the same team of guys. They are definitely casting plate grids, they are pasting them and they are drying plates on a rack. If it is not in this one there is in another video YouTube shows on the right as "similar videos".

I though those videos were made in different places by unrelated people until I say the bearded guy (in white/grey clothing) that was rebuilding a battery at street side in another video that was showing them manufacturing plates.

It is pretty cool they can do it start to finish. I just wish they were more h&s conscious.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 09, 2021, 09:55:24 pm
Regarding the battery I showed the picture off. I had to glue the top back together or the recycling guy wouldn't take it. Before I did that I pulled one of the plate packs and I found something very interesting.

The negative plates were in very good condition. The positive plates were practically gone. Few small pieces remained, but the majority turned to dust.

Why, is this interesting? Well, to me it is because after reading lots of online sources one would be justified in thinking the biggest issue with lead acid batteries is sulphation as a problem with negative plate condtivity. It seems with this very old battery that wasn't the case. It is positive plate corrosion that killed it.

As far as I know, short of replacing plates, there is nothing that can reverse or recondition such corrosion :-(
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 12, 2021, 01:13:09 pm
And another data point.

A car battery was purchased 4 years ago. It is a 75ah battery with 750A CCA (the car has a tdi 2.0 engine so requires a pretty large battery).The car is used rarely, maybe once every 7~10 days for short trips of few km. So a pretty hard life for the battery. Specially in winter. After 2 years the battery wasn't starting the car reliability. I bought a new one and I gave the old one to a friend with an off-grid cabin. He used it in his power bank for 2 summers until it wasn't keeping a good charge. Then recently it came back to me.

Surprisingly after few months in storage it still showed a pretty good voltage of 12.6.the electrolyte measured 1.26. When I shorted briefly it gave me 150amps when cold and almost 300a while warm.

I didn't use the magnesium sulphate with that battery, because I wanted it to be a control for the chemical treatment. I just kept it on a trickle charger on and off for the better part of last 2 weeks. Few days ago I discharged if with 55A to 12.0V and I used my newly built pulse charger. I was using 18kHz pulsing frequency, 5% duty cycle and about 23V which gave close to 5A average current (later I changed the frequency to 1Khz, but that's with another battery).

Another discharge to 12V took 25% longer, but this may be due to temperature difference.

However, I decided to test the CCA differently this time, because my clamp on current meter only goes to 400A.I put the battery in my tractor that usually has a set of two 195ah/1000CCA 6V batteries. I know for a fact the tractor requires ~700 amps at minimum to start. I turned the key and it started as if it had the 1000CCA battery in. I let it run for a bit and I restarted it few times later to test it wasn't a fluke.

So there we have it. CCA of one battery was significantly improved by pulsing and trickle charging for a long time. There is also slight increase in capacity.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 19, 2021, 10:19:43 am
I've built a simple discharge tester so I can measure battery capacity with various discharge currents. I can also set various voltage cutoff points.

With this I measured the 100AH battery that would keep a 12V 40W car light bulb lit for only half an hour when it came to me. I've used magnesium sulphate (10%concentration only) with it and it was on trickle charge for about a week, plus my pulse desulphation was run on it for about 10h.

The battery lasts only 5 minutes when 55A are drawn from iit, but measured with a 55W light bulb until 12.0V cutoff I got 20AH out of it. This would suggest 40ah total capacity currently. The electrolyte measured 1.28 when charged and 1.24 after the 20ah test.

Thats much better than "keeping a 40W bulb lit for half an hour", but the battery seems to exhibit very high Peukert factor. Peukert factor is a way to express smaller capacity of a battery when discharged with higher current.

Unfortunately I can't tell if the reason is sulphation (plates seem to look OK), positive grid deterioration, loss of active material by shedding or something else. (electrolyte seems clear)

I read in an old 1922 lead acid care battery book about another desulphation method. The method involves charging the battery as far as it goes based on electrolyte density then dumping the electrolyte and replacing it with distilled water. Then charging again.

I'll probably try that next.

Title: Re: Reconditioning old/dead lead acid batteries.
Post by: floobydust on December 19, 2021, 08:52:27 pm
Have you considered measuring the battery's ESR? That does flush out mechanical (corrosion) issues as well as sulphation.
There are many automotive car battery ESR meters out there now, instead of doing a hard load test which doesn't differentiate between state of charge and capacity.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 21, 2021, 10:46:25 am
Have you considered measuring the battery's ESR? That does flush out mechanical (corrosion) issues as well as sulphation.
There are many automotive car battery ESR meters out there now, instead of doing a hard load test which doesn't differentiate between state of charge and capacity.

I haven't yet. Good idea.

I'll do some research to find out if ESR of a battery can be measured using the usual measuring equipment rather than purpose built meter. I only have few batteries to check so I would prefer not to buy one (for around $60).
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: HarryDoPECC on December 26, 2021, 12:29:05 am
I'm always in two minds reading "restore lead acid" threads because while it's certainly possible to reverse some of the deterioration, it's also the case that many cells will be more like those torn down by TerraHertz (who is here from time to time):

http://everist.org/NobLog/20180430_lead_acid_ruin.htm (http://everist.org/NobLog/20180430_lead_acid_ruin.htm)

Seems to me that the biggest problem is not designing a reconditioner but obtaining the xray vision needed to decide which cells are even worth a try.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: Fflint on December 31, 2021, 11:50:05 am
I'm always in two minds reading "restore lead acid" threads because while it's certainly possible to reverse some of the deterioration, it's also the case that many cells will be more like those torn down by TerraHertz (who is here from time to time):

http://everist.org/NobLog/20180430_lead_acid_ruin.htm (http://everist.org/NobLog/20180430_lead_acid_ruin.htm)

Seems to me that the biggest problem is not designing a reconditioner but obtaining the xray vision needed to decide which cells are even worth a try.


True, two of my batteries were unrecoverable. Fun fact, I had to glue them back together or the seller wouldn't accept them for exchange / recycling. We have a law here that if you're buying a new lead acid battery you have to return the old one (or pay a fee). So I got two new 6V 195ah batteries.

However, I think I was successful restoring an old 12v car battery (details in previous posts). I have been using it as a starter battery in my tractor for last few weeks and it started the tractor reliably every time (no extra charging required). There were even few starts when the temperature was around - 8C (it is a diesel tractor that usually requires a 1000cca battery).

I'm quite happy with the result with this one.

As for, how to choose the batteries to restore? My advice would be, if you only have few batteries, try it on all of them or do the following :
- open the cap and look inside the cell. Does it look OK, or is it all twisted/deformed?
- can you see heavy grid corrosion with sections missing?
If the answer to the above is yes I would probably not attempt to recover it.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: G7PSK on January 27, 2022, 03:27:10 pm
The best treatment for old batteries is to wash the cells out to clear the debris that collects at the bottom of the cells and shorts them out, then refill with fresh acid. I found that doing this with a bank of large lead acid cells on a wind turbine system (the cells were 900 Amp hour each, every five years the battery bank lasted twenty five years and were still good when the property and system were sold. I have washed out large truck/tractor batteries as well and found that they recovered 80 to 90% of original capacity. But you need to do this before the cells are damaged from being internal shorted. 
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: SilverSolder on January 27, 2022, 03:40:30 pm
The best treatment for old batteries is to wash the cells out to clear the debris that collects at the bottom of the cells and shorts them out, then refill with fresh acid. I found that doing this with a bank of large lead acid cells on a wind turbine system (the cells were 900 Amp hour each, every five years the battery bank lasted twenty five years and were still good when the property and system were sold. I have washed out large truck/tractor batteries as well and found that they recovered 80 to 90% of original capacity. But you need to do this before the cells are damaged from being internal shorted.

How did you wash them,  just rinse with water?
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: G7PSK on January 27, 2022, 06:17:52 pm
Rinse several times with distilled or deionised water. Never use tap water, slosh the batteries cells about the best you can repeat until the water runs clear or clear-ish.
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: f4eru on January 27, 2022, 07:50:08 pm
in which state do you do this, charged or discharged ?
One thing to take care is disposal of the lead contaminated water. Were do you dispose it of ?
Title: Re: Reconditioning old/dead lead acid batteries.
Post by: G7PSK on January 27, 2022, 09:56:11 pm
As is when it becomes necessary to do so whatever the charge state, In days gone by I would just throw some lime in the old acid and water then pour it into a hole in the ground but now I have to take it to a recycling center as what was considered acceptable in the 70's is no longer.