Details of a chemical method for rejuvenating an old battery

You have probably never stopped to consider it, but very few batteries are replaced because they stop working. In almost every case, the battery is replaced because it doesn't work well enough any more. What is not generally realised is that something can be done at this stage which may well prolong the useful life of the battery - quite often by many years, and that the same treatment carried out earlier may well have stopped the symptoms from occurring in the first place.

To understand what can be done requires a simple appreciation of how a lead acid battery works. These batteries are a series of cells; the most common is the 12V type which is six cells in series. Each cell consists of a plate of lead and a supported plate of lead (IV) oxide, both immersed in fairly concentrated sulphuric acid. The lead oxide plate is the +ve. pole, the lead plate is the -ve. pole. As the battery discharges, electrons flow from the -ve. to the +ve. pole; when we charge the battery, we just drive electrons back in the opposite direction.

The reason for a battery failing to work properly anymore is due to the chemical processes which take place within each cell. As the battery discharges, the +ve. plate reacts with the sulphuric acid to produce lead ions and water. The -ve. plate dissolves to form lead ions in the process, which finally leads to the battery's complete failure. On charging, the +ve. plate builds up a thicker coating of lead oxide, removing water and lead ions from the sulphuric acid as it does so. The -ve. plate fizzes and releases hydrogen from the sulphuric acid as it builds up a coating of lead.

It is the lead ions formed in the discharge cycle which cause problems. They combine with sulphate ions in sulphuric acid to form highly insoluble lead sulphate. When this coats the plates of the battery, it fails to deliver enough power to be of use although it may well be thoroughly serviceable in every other way; only the 'sulphating' stops the battery delivering enough power to start the vehicle.

The sulphating can effectively be removed or prevented by adding to each cell a weak organic acid, ethylene diamine tetraacetic acid, known to chemists as EDTA. It is a complex analytical reagent which forms co-ordination compounds with many metal ions, including the lead ions formed in the discharge cycle of a battery. The compound formed by lead ions and EDTA is very stable in alkaline solution but not in the acidic medium of a battery: this is extremely fortunate. As EDTA forms a compound with the lead ions in the lead sulphate on the battery plate, it breaks down again. EDTA and lead sulphate are regenerated, but this time the lead sulphate doesn't coat the plate, it sinks down to the bottom of the cell where it lies harmlessly since it doesn't conduct electricity, and the EDTA is free to continue its work. What EDTA effectively does then, is free the plates of sulphating.

As can be seen from the above, treating a battery with EDTA is likely to be most effective when the battery, for one reason or another, spends periods when it is not fully charged, and so contains too many lead ions. This is likely to occur if the vehicle is used just for short trips, is infrequently used, or suffers from an inefficient dynamo or alternator.

To treat a battery with EDTA you add about a rounded teaspoonful of the powder to each cell - this assumes an average sized battery, but the exact amount is in no way critical. You should use the vehicle normally for a while or agitate the battery frequently for a few days, then give it a thorough charge to build up on the cleaned plate areas. On the assumption that sulphating has been affecting the performance of your battery, an increased performance will be noted from here on.

On my system, electronic pulsing is accomplished by pulsing with a modified Don Denhardt thermistor controlled pulser. It's just a matter of leaving the pulser connected long enough to erode the sulfate crystals back into the electrolyte. From a couple of days to a month, depending on the amount of sulfation you want to remove...The last 10% is hard to remove and takes longer than the first 90%.

I sometimes use EDTA on the really badly sulfated batteries, when I don't want to waste a month or two on it with pulsing. The fastest way is to empty out the electrolyte and flush the battery with distilled water, then desulfate with EDTA. I just pick the battery up, turn it upside down and shake it to get the fluids out. It's a lot of work, but it works fast...but be aware that it is harsh and dangerous, with a higher failure rate, due to the plates breaking down and shorting out. Acid gets on you; You must keep it flushed off with lots of water. I repeat, it is harsh and dangerous...I don't encourage this method, but is useful in culling otherwise useless batteries for desulfation. Shorted batteries are never candidates for desulfation. Don't mess with them. If you find a 12V battery with less than 10.5 volts, I almost guarantee one or more of the plates are shorted. I won't touch a battery that is lower than 11.5V as a rule. I have heard of adding baking soda (sodium bicarbonate) in the distilled water stage to further raise the ph, to speed up things...but it is a nightmare of flushing with distilled water, to get the bicarb out. Otherwise, it's a waste to add fresh electrolyte. I wouldn't recommend it at all. Even though I buy distilled water at Walmart for 58 cents a gallon, I would have to use 10 gallons of flushing and my arms would fall off from the shaking and it's not worth it.

The Process:

I first shake the battery around to loosen the shedded plate material on the floor. After shaking the electrolyte and debris out, I fill it halfway with distilled water, shake it around and empty it out while shaking. After flushing a couple of times with distilled, the water comes out fairly clean. I then fill it with distilled water, add the EDTA (dissolved with distilled water) and let the battery sit for a couple of hours. If it is badly sulfated, it will immediately bubble like the devil from the chemical reaction. After the resting period, I then put a 2 amp charge on it and usually add the pulser to help it along. After a day or so, the voltage hits 12.5V and plates are nearly cleaned. I then let it sit for day, with only the pulser on it. The voltage usually drops to 10.5 or lower. I pull the pulser and charger, and connect my 100 or 50 amp load tester (depending on battery type and size). After a couple of 10 second tests, to check the condition, I run the battery down further for a couple of minutes (about thirty seconds at a time, to prevent overheating the load tester), to drain it down. Apparently, the desulfation process works quicker when the battery has been quickly drained and is slow charging again (this also works in pulsing alone). I've use a heavy steel tire iron across the posts for 10-15 seconds on non-desulfated batteries and recharged. Doing this (hot discharge) on any lead acid battery, at anytime, (with or without EDTA or pulsing), filled with regular electrolyte or distilled water, will always cause the amount of reserve current to rise. This can always be verified when later charged fully up and tested with a load tester...It probably exposes more fresh plate area. This rough treatment also will kill a battery with crumbly plates and weak separators. It may cause the battery to blow up, especially if the electrolyte level is low (more room for hydrogen and oxygen gas to accumulate-that's another reason to keep the battery topped off with distilled water) ...Don't be tempted. Acid is nasty to the face and eyes. A battery with the water level lowered to the top of the plates has enough trapped gas to explode the battery like a small bomb....That's no exaggeration...I've seen it happen.

I then drain the distilled water thoroughly, add fresh electrolyte and let the battery rest for a couple of hours. The final act is to recharge the battery up to 13.5V on a long slow charge. About seventy five percent of the shorts will show up now. Most of the tears in the plastic separators were hidden by the sulfate crystals. Lead sulfate crystals act as insulators, keeping the swollen or crumbly plates from touching. When the crystals are gone, any deformaties in the plates, along with tears in the separators, will cause the plates to touch and short when charged up to about 12.5-12.75V. If the battery passes these rigors, it is going to live for a long while.

Remember, the batteries I use this harsh method on are old and badly sulfated to begin with; non-shorted junkers. I want to weed the terminal ones out, right then, and not even save the marginal ones, which are going to short and die six months or a year down the line anyhow.

Good candidates for desulfation are relatively young batteries, that have become sulfated thru neglect and extended discharge. A new battery can become completely sulfated if left nearly fully discharged, in only a couple of weeks. The plates are fairly new, but covered in crystals. These newer batteries better respond to any type of desulfation with a lesser rate of shorts.

If you have the time, electronic desulfation usually the safest method. The next safest method would be to add a small dose of liquid EDTA to the old electrolyte and let it work slowly over time. EDTA doesn't like to dissolve in acid. If you start with powdered EDTA, dissolve it in very warm distilled water. EDTA works slowly in an acid environment. After removing the crystals, most the EDTA/crystal compound breaks down in the acid and some of the EDTA is free to work again. It permanently bonds in a non-acid environment, but works quicky.

I prefer electonic pulsing over EDTA, because when the eroded crystals dissolve, the sulfate is released back into the electolyte and some of the lead or lead peroxide plate material is "plated" back onto the respective plates, the rest settling onto the floor of the battery case. More of the plate material ends up on the floor with the use of EDTA, but most batteries have an excess of material to start with, and full current reserve is maintained. The exception are very old batteries, where most of the plates have already shedded on to the floor to begin with and the desulfation process reduces the plates down to nearly the capacity before the desulfation began. Toss'em in the recycle heap and find a better candidate to work on.

The bottom line is, if you wait too many years to begin any type of desulfation, the battery probably won't be worth the effort. I'd start pulsing batteries within six months, to a year of use, for at least a day or two.

Desulfation works best in higher temperatures. The best time to pulse your batteries in your vehicle and battery bank is summer. Make it a habit to pulse all of your batteries every summer and you will extend the life of them four or five times...Eventually, enough of the plate material will shed off to the point where the battery's reserve is reduced to 50% of the original reserve...That is the time to send them off to the recycler... not because of deep sulfation, or shorts caused by sulfates swelling the plates, crumbling them and rupturing the separators.