Sciencemadness Discussion Board

Reversing Lead Sulphation on Battery Plates

Chris_H - 2-12-2016 at 16:52

Hi All Merry Christmas (Yep they go around Faster & Faster!) I am new here so don't be harsh on me please. I am interested in Lead acid battery tech. These batteries are constrained by a chemical reaction that can (if left in discharged state/eventually leaves the negative Pb plates sulphated. The more sulphation the less capacity as the sulphation acts as a barrier. The general chemical equation for this type of battery I believe is : (Charged state) Pb(s) + PbO2(s) + 4H+(aq) + 2SO42-(aq) → (Discharged state) 2PbSO4(s) + 2H2O(l) E ~ +2 V. Apparently introducing sulphates to the electrolyte such as Sodium sulphate, Magnesium sulphate, Aluminium sulphate hydrated with distilled water can remove some of the sulphation on the negative battery plate to become a Bisulphate, I am not sure if this is (aq) or a (s)? Can anyone with some working knowledge give me a chemical reaction/equation that can justify this? Here is a rather good link with some further information on the process:
http://www.rainingspiritdojo.com.au/downloads/alternativelea...

I'd be extremely grateful if any chembots out there could clarify if this is actually possible? Thanks all :)

XeonTheMGPony - 3-12-2016 at 07:49

Once they are sulfated too badly battery is toast.

But if the battery is worth it:
Note Sg = Specific Gravity

Dump out electrolyte into a large bin, rinse the battery thoroughly with distilled water and dump into previous electrolyte.

Set battery aside, Now filter thoroughly the electrolyte then boil to concentrate, Filter this yet again then bottle and set aside.

Back to the battery: fill all cells to the proper height with pure distilled water, attach a charger and bring the voltage to what ever is needed to get it to 5amps charge rate and place a glass therm in the middle cell to monitor temps.

Monitor the amps and temp of the battery, Check the Sp of the cells as well, as the hard sulfate dissolves in the water the amps will go up along with the Sg.

If the Sp goes up past 1.2 you have hard proof some one has added acid and not water to the battery at some point, drain and refill with distilled water and continue this process till the Sg does not rise in any of the cells.

Get your bottle of concentrated acid, read the manufactures rated Sp of electrolyte at full charge, with clean water mix your acid to water to the correct Sp then fill the battery, place on an equalizing charge (for a 6v that is 7.5v, for a 12v that is 15.5V)

Charge untill all cells are freely gassing, take off charge and allow to rest for 1h, then measure all the cells Sg, adjust as required.

Do do this will eat up an entire day if not 2, So usually not worth the effort for any thing less then a quality 8D battery or a traction cell.

But if just messing around why not, but for starter batteries this won't do mush as they simply disintegrate, so there is just nothing to desulfate, this is meant for traction batteries or deep cycles.

XeonTheMGPony - 3-12-2016 at 07:52

All so adding any crap to your battery, Congrates you're screwed! DO NOT DO IT EVER! less it is a dire emergency and you plan to replace the cell, but I live off my batteries (Solar system) So I don't put them at any risk what so ever!

Lead batteries are sturdy critters but there are allot of land mines in their care that can be counter intuitive, you have to look at them as the whole not at any one factor (Mistake that most make)


The only thing you should ever add to your battery is water and energy, nothing more, proper equalizing charges and a good charging system will prevent any hard sulfates from forming, and never pulling more then 50% Depth of discharge will give them a long life!

[Edited on 3-12-2016 by XeonTheMGPony]

Chris_H - 3-12-2016 at 16:06

Thanks for taking the time in offering your advice XeonTheMGPony, I will definitely give this a go:). It may take me some time but I'll leave you some feedback on my results. My battery is a 48v 633Ah traction battery (24x2V) cells, so this process will take me quite a while I'm guessing! Quick question? Will distilled water at 5amps remove hard sulphation alone?

XeonTheMGPony - 3-12-2016 at 19:59

Yes the hard sulfate is far more soluble in pure water, won't be super fast but with monitoring it will eventually break, you'll see amps start to climb as it dissolves.

Care full monitoring is the key. basically push what ever voltage you need to keep a steady 4/5amp trickle

Deffenitaly worth the effort with those Cells!, Charge them up as much as possible first too, speed things up.

Chris_H - 4-12-2016 at 06:28

Thanks again for your advice!

Cheers Chris

roXefeller - 8-1-2018 at 10:47

That's a great description of desulfation. Since you live off of lead acid batteries, are you able to speak to whether batteries require a temperature compensated charging voltage. The source I took this from is attached. And other sources below. Is this true of the battery chemistry or just a selling gimmick?

http://batteryuniversity.com/learn/article/charging_at_high_...

http://solarprofessional.com/articles/design-installation/un...

Attachment: 5-How-To-Specify-a-Genset-Battery-Charger.pdf (217kB)
This file has been downloaded 549 times

Fulmen - 21-7-2021 at 12:11

I just kickstarted a couple of 20Ah AGM batteries, I'm actually a bit surprised it worked.

These are scooter batteries a friend killed by leaving them discharged outside for the winter. Now they wouldn't take a charge at all.
So I added some water and fired up the 6-80V PSU. At 85V I managed to get a couple of milliamps going. I limited the current to 100mA, and after a few minutes the voltage started dropping slowly. After appr one hour the voltage was down to 14V, I then switched to max 14V and max 2A. After 3 hours the second battery is already at 0,5A. The first one was done in increments so I don't have a complete time record of that, but I stopped after 10hours @2A. I'm now leaving it over night to see if it's actually holding a charge.

Is there any hope for these?

XeonTheMGPony - 21-7-2021 at 18:16

Quote: Originally posted by roXefeller  
That's a great description of desulfation. Since you live off of lead acid batteries, are you able to speak to whether batteries require a temperature compensated charging voltage. The source I took this from is attached. And other sources below. Is this true of the battery chemistry or just a selling gimmick?

http://batteryuniversity.com/learn/article/charging_at_high_...

http://solarprofessional.com/articles/design-installation/un...


Voltage deff needs to be adjusted for temperature, so any controller that does it well is well worth it.

XeonTheMGPony - 21-7-2021 at 18:18

Quote: Originally posted by Fulmen  
I just kickstarted a couple of 20Ah AGM batteries, I'm actually a bit surprised it worked.

These are scooter batteries a friend killed by leaving them discharged outside for the winter. Now they wouldn't take a charge at all.
So I added some water and fired up the 6-80V PSU. At 85V I managed to get a couple of milliamps going. I limited the current to 100mA, and after a few minutes the voltage started dropping slowly. After appr one hour the voltage was down to 14V, I then switched to max 14V and max 2A. After 3 hours the second battery is already at 0,5A. The first one was done in increments so I don't have a complete time record of that, but I stopped after 10hours @2A. I'm now leaving it over night to see if it's actually holding a charge.

Is there any hope for these?


Winter may be the saving grace here, and AGMs have been known to recover from a one off, so there is a shimmer of hope, you'll know after a few cycles. Worth trying for sure.

Fulmen - 22-7-2021 at 00:43

It does look promising, after resting overnight the first holds at 11.7V and seem to handle a quick 1A load just fine. The second battery reached 0.8A before shutting down for the night, this morning it started at 0,3A, rising slowly. Could be a temperature issue.

It's going to take time to get through all 4 batteries. The PSU could handle all 4 in series but I think it's safer to do them one at a time. Since I can't change the electrolyte or even test the density it's hard to monitor the process properly. Better safe than sorry I guess.

I'm also seeing a 0,4V discrepancy between the DMM and the PSU, not the end of the world I guess but still annoying. Is there any simple and reliable voltage references one could cook up at home? Most electronics is ±5% so that's of little use.

Twospoons - 22-7-2021 at 12:59

Quote: Originally posted by Fulmen  
Most electronics is ±5% so that's of little use.


I disagree. We use 1% parts as standard these days - for resistors at least. Tighter tolerances are readily available, though if you want 0.01% or better its going to cost you.

Your 0.4V difference may come down to contact/lead resistance x current. Or your DMM battery may be low - really only an issue with the cheaper (generally Chinese) models.
Or your PSU readout simply isn't calibrated at all.


If you want a reference voltage source there are 0.1% chips available for a buck. Look on Digikey or Mouser.

Given the nature of this forum, you possibly have everything you need to make one of these: Clark Cell



[Edited on 22-7-2021 by Twospoons]

Fulmen - 22-7-2021 at 13:13

I know everything is available on order, but that takes ages these days. And I'm not looking for another electronics project right now. 1% is good enough for this use.

Edit:
I've looked at both the Clark and the Weston cell, but I won't handle mercury (or it's compounds) with my current setup.

[Edited on 22-7-21 by Fulmen]

Fulmen - 24-7-2021 at 01:03

I tested a handful of LM78xx regulators, and the DMM reads 4% low on all of them. That's good enough for now.

As for the second battery I haven't had time to give it an "all day charge" yet, I won't do this unattended. After several shorter sessions I'm up to 0,65A @14V, (starts at 0.8A), the voltage is still low (10,6V immediately after suspending the charging). No obvious signs of gassing, but I'm not quite sure how to judge this on a AGM. I do have a refracting acid tester at work, but is is at all possible to get a usable sample out of these batteries?

XeonTheMGPony - 24-7-2021 at 05:29

on the top there will be a glued on strip, under this strip will be the cell wells covered by rubber caps and that will give you access to the internals

Fulmen - 24-7-2021 at 06:23

I know, but there is no free liquid in AGM batteries.

Fulmen - 26-7-2021 at 01:21

Working on the last two batteries now, they all seem to be salvageable. After getting them down to appr 30V@200mA I hooked them in series to save time. So far the batteries hold the same voltage ( ±1V or so).

As for the batteries I'm a bit uncertain if it's gel or AGM. Apparently the mfg has two different batteries with the same designation:

https://www.chilweebattery.com/motive-power-battery/electric...
https://www.chilweebattery.com/motive-power-battery/6-dzf-20...

The colors match the second one (Gel - green/black casing), but the marking is different (just model number and "valve regulated lead acid").

Fulmen - 4-8-2021 at 12:33

Some of the first thing I did has come back to bite me in my ass: I added water! Aw crap...

Status: All batteries have been recharged to (roughly) <200mA @ 13.5V, open voltage 12-12.5V, and seems to be holding. Now I'm starting topping them off, which should be <280mA@14.6-14.8V (28Ah@20hr AGM). But since I stupidly added water when trying to revive them, the first battery "spilled over" and has leveled out at 600mA@14.6V. So I guess I'm low on acid, right? So how do you adjust acid density on AGM batteries? I do have access to a refractometer at work, so I only need a few drops. Can I just turn it upside down into 6 cups?
I also need to homogenize the cell afterwards, right? And how do I "level" the cell?

macckone - 5-8-2021 at 08:20

There are battery chargers that have a specific setting to remove sulphation.
I suggest using one of those in most cases.
You should never add acid to a battery unless it is spilled or has never been filled (large cells are unfilled in transport).
Sulphuric acid does not evaporate, water does.
Some sulphuric acid can break down but it is minimal.

AGM cells have very little water to begin with and if you add too much water it is doubtful much sulfuric acid actually spilled as it is trapped in the matt. It is possible more spilled than I am suggesting but it sounds like the battery should be left to sit for 24 hours and see where it is.

Leveling is short bursts of low current to top off each cell so they are all equal.

Fulmen - 5-8-2021 at 10:54

I'm afraid I've lost a significant amount of acid. I added a fair amount of water, and when it started overflowing during charging I sucked up the excess and (thinking same as you) dumped it in a can with dilute acid. The smart thing would probably have been to boil it down and add it back.

Edit: The battery behaves the same today, it levels out at 0.55A @ 14.6V
It has dropped 0,05A in some 4-5hours charging, supporting my theory that it's gassing off water.

What I meant with "leveling" was adjusting the amount of acid. As I understand AGM the mat isn't fully immersed in acid, it's more like a moist towel to allow for gassing. One solution would be to overfill, then charge and siphon off the excess during gassing. But it's a bit labor intensive, I would have to do a full discharge/recharge to be sure it's safe.

[Edited on 5-8-21 by Fulmen]

macckone - 5-8-2021 at 12:00

if you are getting gassing it is probably mostly hydrogen and oxygen.
If you are getting sulfide smells then the battery is probably toast.
The mats are definitely like a wet sponge. There usually isn't a lot of free liquid in the battery.

There is not an easy way to tell what is needed in AGM batteries.
They are not designed to be maintained.

I would keep charging until it explodes or the amperage drops.
From the sound there is way too much water in there which is causing the high current.

Ultimately you are trying to recondition a dead battery and it may remain dead.

Fulmen - 6-8-2021 at 05:37

It's definitively not dead anymore, but it's a set of 4 so ideally they should be in equal condition. I think you're right in that they will level out with enough charging, but that will take weeks for sure. Adding acid should shorten down that time considerably, and as long as I add the same amount of acid to all cells I shouldn't do any real damage.

Update: I boiled down some battery acid to at least 60%, then added 5ml to each cell. I'll leave it overnight to homogenize before resuming charging.

[Edited on 6-8-21 by Fulmen]

Fulmen - 9-8-2021 at 11:22

That little test didn't do much of anything, so it's time to get more data.
I was able to extract a few ml's from each cell with a pipette after charging it until it started gassing. I'll try to test the acid tomorrow, but I also need to estimate the amount of acid I'm dealing with. Maybe there is some simple rule-of-thumb for this, but I haven't found one yet. But it should be possible to calculate the number of mols of H2SO4 consumed per Ah, right? IIRC the amount of charge needed to restore a completely discharged battery is appr 2x the rated capacity, which seems to fit my experiments fairly well...

Fulmen - 11-8-2021 at 10:17

I finally have some data:
Cell Sp.gr
1 - 1.29
2 - 1.32
3 - 1.29
4 - 1.28
5 - 1.30
6 - 1.33

As for the amount of acid my reasoning is as follows:
28Ah (@20hr) = 100800C = 1.04mols of e- = 0,52mols H2SO4 = 51.2g H2SO4. Assuming a charged density of 1.3 (40%, 521g/l) and a discharged density of 1.1(15%, 165g/l) I get a volume of 144ml. Does that sound reasonable?