Lead acid batteries often die due to an accumulation of lead sulphate crystals on the plates inside the battery, fortunately, you can recondition your battery at home using inexpensive ingredients.

A battery is effectively a small chemical plant which stores energy in its plates. They are chemically charged with an electrolyte which is a mixture of distilled water and sulphuric acid. When the battery is discharged, the lead active material on the positive plates reacts with the sulphuric acid and produces lead sulphate. When the battery is charged, this process is reversed and the lead sulphate crystals react to form sulphuric acid again. The battery fails when there is an excess build up of lead sulphate crystals which then do not allow sulphuric acid to make contact with sections of the plate. These crystals harden and eventually cause a chemical imbalance in the electrolyte.

crystals on battery plate

In most cases, hardened crystals can be removed using a solution of magnesium sulphate. This method doesn’t restore a battery back to original condition but it will restore it to around 70-80% of its original capacity.

What You Will Need To Recondition Your Battery

  • The Damaged Battery
  • 400ml (12oz) Distilled Water – Buy Here
  • 200g (7oz) Epsom Salts (magnesium sulphate) – Buy Here
  • A Syringe or Dropper – Buy Here
  • A Battery Charger – Buy Here

How To Recondition Your Battery

battery before

Take the battery out of the vehicle and put it onto a solid work bench.

battery opened

Some battery’s cells are clearly visible on top of the battery and are sealed with screw in caps. Others, like mine, are protected by a “sealing” strip. You may need to cut the edges of this strip to get it loose but it is almost always removable. Once this has been removed, you will also need to take the caps off each of the individual cells in order to get to the battery acid.

battery removing water

Using a syringe or dropper, carefully drain each cell one by one until they are all around 50-60% full, if some cells are already lower than this then exchange some acid from the fuller cells. You don’t want to take too much out as you will then struggle to charge the battery again. The liquid you are removing is a strong acid so put it into a glass container and be careful not to mess any of it on your hands or clothing.

Make sure that you dispose of the removed battery acid in a safe and responsible manner. The removed battery acid is extremely corrosive and contains heavy metals, mainly lead.

epsom salt solution

Now you need to make a saturated solution of Epsom salts (magnesium sulphate) and distilled water. Do this by boiling water and continuously stirring in more salts until no more will dissolve in the water. Then fill each cell with the Epsom salt solution to the full level line with the syringe or dropper.

charging battery

When charging the battery while it is being reconditioned, some gas will be released so it is advisable to leave the caps open. Connect a battery charger to the terminals and let it complete the charging cycle. If the battery is heavily drained or damaged, it may have to be charged overnight with a trickle charger at a very low amperage. If you do not have a battery charger then replace the battery cell caps and covers and reinstall the battery in the vehicle. Jump start it and then take it for a half hour to a full hour drive to allow the battery to charge using the alternator.

clean up battery

The reconditioned battery should now last another 6 months to a year and can usually be restored using this method about three to five times until it is no longer effective.

Edit: As some users in the comments section have suggested, the best solution would be to let the reconditioning process run for a few days to properly “clean” the plates and then drain the Epsom salt solution from the battery and replace it with the recommended 35/65 acid solution.

Have you tried to recondition a battery using this method or a similar method? Let us know in the comments section below.

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60 Replies to “Recondition a Lead Acid Battery, Don’t Buy A New One”

  1. About 15-16 months ago I added distilled water to my cars completely dead battery. I happened to have a charger that loved to overcharge, causing the batteries electrolyte to boil. I continued to overcharge and top of the fluid (in a vented area, of course). This was a test to see if it would clean hardened lead sulfate from the internal plates to extend its life. The battery lasted till this winter before drastically losing its capacity.

    So I’d like to safely create my own solution of battery acid mixture – just like humanity did when lead acid batteries were serviceable in the early days. I don’t see that topic covered too often.

  2. I red some good methods for reconditining batteries, we can do it at home and save a lot of money. No need to throw out old batteris and i beleive these methods will helps to start a new business also. I belive this is a good guide (step-by-step guide).

    1. Hi Otto,
      No you can’t use ordinary table salt. Table salt is chemically very different to Epsom salts and the process involves a chemical reaction to clean the plates within your battery which won’t work with table salt.

    2. MgSO4 (epsom salt or Magnesium Sulphate) vs CaCl (table salt)
      H2SO4 (sulfuric acid)
      PbSO4 (Lead Sulphate)

      The idea is to use MgSO4 a highly soluble salt to pull the PbSO4 crystal off the plate.

  3. I initially posted back in January. Since then, I’ve done a lot of research and have done a bit to recondition several of the batteries I have that hold a poor charge. I attempted the Magnesium Sulfate method (Epsom Salt dissolved in distilled water). This is only a temporary solution to allow electrical current to pass through the hardened lead sulfate insulator. It also helps break up the lead sulfate once it accepts the charge and is properly recharged. However, it seems as if the magnesium sulfate shortens the life of the battery afterword.

    I began to (using proper PPE) siphon the discharged sulfuric acid from a couple cells and noticed that the plates were breaking in to chunks. So the plates themselves are very fragile apparently. That battery was definitely no good at that point. The local automotive stores here sell battery fluid acid (30-38% sulfuric acid) in a 6 quart box sealed inside of a HDPE (plastic) bag. Generally, certain HDPE’s are storage for sulfuric acid. My next effort is to clean out a battery that has plates in good condition. Safely of course.

    1. Hi Jack,

      Thank you for the great feedback. It would certainly be interesting to do some testing on a range of new and reconditioned batteries to determine the effect on the life of the battery after performing this “reconditioning”. I’ve done this process on two or three batteries now and they’ve all lasted around a year after the re-conditioning although they have all been the smaller motorbike batteries as shown in the images here. Perhaps a larger vehicle battery degrades faster.

      Please let us know how your cleaning out exercise goes, I’d love to include a follow up with some images on what you’ve found!

  4. We have a vw polo 6R. The battery died and went to test it. They said we must buy a new one. After seeing this post we’ve tried it on the old battery. And it is working like a charm. Thank you for your advise and saved us some money

    1. Hi Pieter,
      Thanks for the great feedback! I’ve found that I can get at least a year or two of additional life out of my motorbike batteries using this process, it’s definitely saved me a lot of money over the years!

  5. Hi I’m going to give it a go tomorrow but after I’ve completed the epson salt thing I’m going to put fresh acid solution back in the battery
    The battery will go to full charge but just doesn’t have any guts
    I hope I’m not disappointed
    Cheers stu

    1. Hi Stu,
      Going to full charge but not producing any current makes a pretty good candidate for this reconditioning process. You can replace the battery acid eventually but rather leave the epsom salt mixture in the battery for a few weeks to assist with breaking down the lead sulfate crystals. As soon as you remove the epsom salts, you’re stopping the crystal removal process as well. Good luck.

    2. No need to add fresh acid solution to the battery. The sulfuric acid in the battery breaks into sulfur which reacts with the lead to make lead sulfide. Epsom salt is magnesium sulfide and has the same sulfur that the acid does to react with the lead. It is just as effective.

    3. i did the same think with the epsom salts with no luck im going to drain it out and put new acid and recharge and see how it goes

  6. How do I safely dispose of the old acid I’ve removed from the battery?

    This is an excellent post with good comments. Thanks all!

    1. Hi Denise, thanks for the great feedback. Fill a bucket with water and then slowly add the acid to the water while stirring. After that add a teaspoon of baking soda at a time again while stirring until you stop getting a bubbling reaction. This should neutralize the acid and it can then be poured out in a bare patch in the garden or down the drain.

      1. This reply is correct, but it’s important to state that you should never add water to acid (only the other way around). The reaction is very different and extremely dangerous.

    2. Add enough baking soda which will neutralize the acid. A lot of gas will be produced so do this in an open area.
      Its like taking baking soda when you have stomach acid reflux. You start burping!

  7. Can you use the acid you took out of the battery and use it as a drain for as net to unclog drains?aren’t there commercial drain cleaners that are made with sulfuric acid?

    1. Hi Bill,
      There are quite a few commercial drain cleaners which are sulfuric acid based, these would however be used by individuals who are qualified to work with it. If you do use it, use it with extreme caution. It is very corrosive and there are a number of safety risks which need to be properly managed.

    2. I haven’t sharpened up on my battery knowledge lately but I’ll explain what I can recall. Once the mixture of h20 and sulfuric acid are injected in to the battery and an electrical charge is introduced across the terminals, the hydrogen and sulfuric acid chemically react with the batteries lead plates.

      The sulfate ions become negatively charged while the hydrogen ions become positively charged. What happens when the battery is losing its charge? Through chemical reaction, the sulfuric acid begins to react with the lead plates and forms in to lead sulfate (the white powdery substance you may see on a battery terminal).

      So if my memory serves me right, a well discharged battery would have lost its initial acidic strength. I have removed the “electrolyte” from a battery but I did not stick my fingers in there to test the level of acidity.

      So yes, you probably could clean out a drain with battery “electrolyte” if the sulfuric acid is present. Is it going to work as well as drain cleaner? No. The sulfuric acid content in a battery is 30-38%. Some drain “uncloggers” are advertised as 95% sulfuric acid.

      Lead sulfate is also hazardous. That’s something you definitely wouldn’t want to dump down your drain and introduce to the water system and environment.

  8. Hi The DIY Life i would like to know that after i desulfate the battery should i leave the Epsom salt electrolyte inside or i mus remove it and put fresh sulphuric acid? And if so how long must i leave Epsom salt in the battery after reconditioning?
    Thanks Regards

    1. Hi Tinashe,
      Once you’ve run through the slow/trickle charge process and your battery is fully charged again. Remove the liquid from the battery and replace it with fresh sulphuric acid for the best results. You only need to leave it in for a full trickle charge cycle.

      1. Ok thank you i have done my battery today so tomorrow i must remove the liquid? And after taking that liquid out must i put it on charge again when i put new sulphuric acid

        1. Yes, if your battery charger has finished charging the battery tomorrow then you can remove the liquid. You can put it on charge again after swapping out the sulphuric acid, it will probably be almost fully charged already anyway.

  9. Last year I performed this process on a 7 year old battery that would not start my truck. The plates were smothered. The process worked and if fact the battery seemed stronger than it was when new. I worked in the industry of battery chargers for led acid batteries for 4 years. I’m very familiar with charge, float and gas stages of battery maintenance. My company developed a very special and unique stage know as pulse charging. It’s like hitting the plates with a hammer to crack and weaken the dendrite crystals formed during the sulfation phase. Even with my background I never knew you could do this! I doubted it would work. I think its just something the battery industry want’s to keep secret.

    I’m started the process on the same battery after the truck sat for 9 months without charging. I will let you know how it turns out. Theoretically as long as the plates and the plate doping are in decent shape there should be no limit to how many time the process can be performed.

  10. I did two of my batteries now i didn’t come right and i don’t know where i lost it can you please send the whole process of how its done and measurements of Epsom salt with water

  11. Hello, very interesting post. I know that, when charging a battery, a good indicator that the charge is working is the generation of small bubbles (of hydrogen if I’m not wrong). Last night I was charging my car’s battery and I noticed that one cells is not making any bubbles, is this because of hardened crystals or is it another cause? Thanks in advance.

    1. Hi Xavier,
      Yes that sounds correct although there shouldn’t be excessive bubbling, just a few tiny bubbles. It could be due to crystallization or through corrosion of the cell connections or some other problem with the cell. It only really tells you that the cell isn’t charging properly, you can’t really determine why without taking the battery apart.

  12. Xavier should throw that battery out as a defective cell cannot be resolved. It is probably shorting out due to the piling up of debris from the plates on the cell floor, thereby touching the lower plate extremity.
    I have heard of washing out the debris and refilling to spec and recharging.

  13. Can we use use sulpheric acid to recondition the old battery. I want to recondition sealed lead acid 6v 12v batteries. What happen if I use sulpheric acid instead of distill water and epsom salt.

    1. Hi aakash Epsom salts must be used to create the necessary chemical enviroment for the decrystalization of the plates to be a success.

  14. I drained my motorbike battery that did no longer held a charge. Then I filed it with 110% seawater and charged it for about an hour. It tested 12V. Instaled it in my bike and it stated after about a minute cranking. the next day it stated as if the battery was fully chaged.
    how long will this work with the seawater electrolite..?

    1. Hi Alternativejp,
      I have never heard of anyone intentionally putting seawater into a battery and I’m not sure why yours worked, chemically it doesn’t really make sense. Passing any electrical current through salt water is not the best idea as it produces chlorine gas.

  15. It works. . . I measured voltage of a 12 volt battery at 5 volts before unloading the old solution until the top of the plates. I then added the epsom salts solution and measured the voltage. It increased to 12 volts even without charging. Wonderful . . . Thanks for sharing .
    .

  16. There is a man on the internet who swears by first filling the battery with soda and distilled water, charging, emptying and repeating until all the black runs clean. He said the charging was important to clean the plates. Then after rinsing with distilled water, he did the Epson salt with distilled. He said he has done completely dead batteries. He put it back in his riding lawnmower and it started right up. He seemed to think the soda charge was the most important cleaning step.Cayman

  17. Question and confirmation regarding “discharge then recharge” after “reconditioning”.
    I have a portable photography battery pack that uses 12v lead acid batteries which have now died. The batteries are in enclosures which slide into the photo power pack for easy battery change out. I removed the battery from the enclosure and added distilled water to the cells but they will not hold the 12v recharge. Reading your post it is my understanding that I must “recondition” the cells, however, I am concerned about the gasses and discharge/recharge while in the enclosure AFTER “reconditioning”. I just want to confirm that I must now:
    A) Remove the liquid in the battery and neutralize with baking soda for disposal.
    B) Add the distilled water and Epson Salt mixture for reconditioning
    C) Charge the battery full
    D) Remove the reconditioned liquid in the battery and neutralize with baking soda for disposal
    E) Add ONLY distilled water and recharge
    Again, my concern is the use of the battery and possible gases AFTER the “reconditioning” since the caps would now be back on the battery and battery is placed back into the enclosure.
    Other posts seem to recondition the battery and leave the same liquid in the battery after the process. Since the battery is constantly discharging and recharging one would think that gasses would again be produced and cause possible damage. Any comment or direction is appreciated.

    1. Your basic understanding is correct. Depending on the severity of the deposits in the cells, you may want to run them through a discharge and recharge cycle two or three times with the epsom salt solution before emptying them out and replacing the distilled water.

      With regards to the gases. Try keep them open and in a well ventilated place when doing the reconditioning. When you’ve put the distilled water solution back into the battery they’ll be fine again. For your application I wouldn’t suggest leaving the epsom salt solution in the batteries as it does generate a lot more gas when charging. Lead acid batteries, although sealed, do have small ventilation holes to release gases generated when charging or discharging.

  18. Great article and comments. There are some discrepancies between the many modified instructions in the comments. Sometimes it’s recommended that after some time reconditioning the battery with the epsom salt solution to then remove that solution and then restore the battery “fluid” with an acid solution. Other times the recommendation is to (after reconditioning) replace the epsom salt solution with just distilled water. I’m having a hard time believing that if replacing either the acid or epsom salt solution (after reconditioning) with 100% water that the battery fluid will ever return to it’s normal acidity (35% sulfuric acid / 65% water). Should not the replacement fluid after reconditioning be the 35/65 mixture or some other ratio? Is the correct ratio dependent on other factors like the condition of the plates, etc? All comments/suggestions are appreciated. Thanks.

    1. I think the best method is to recondition the battery wit the epsom salt solution and then remove the solution after some time and replace it with the recommended (35/65) acid solution. Simply replacing the solution with distilled water will lead to very poor battery performance, as you’ve stated. In theory you can also simply leave the epsom salt solution in the battery, although performance will be slightly lower than if you replace the solution.

  19. what i don’t understand is how the chemical reaction of converting lead sulfate. to sulfuric acid is supposed to take effect once you remove the sulfuric acid and replace it with (epsom salt) Magnesium sulfate. to my understanding the epsom salt just helps clean the stuck lead sulfate off of the lead plates and converting some of it back into sulfuric acid.
    it sounds to me that we will have a low concentration of sulfuric acid left in the battery.

    would it be better to clean the inside of the battery with epsom salt like you show, but then to drain it, and replace the sulfuric acid with new acid?

    1. Yes you are correct John. As per some of the other comments here, the best solution would be o replace the sulphuric acid afterwards.

  20. Have tried to recondition my N70 with Epson and when I tested it was
    showing 12v but it can not start my car what could be the problem and how can I fix it?

    1. Hi Luguza, did you retain some of the battery acid during the process? Did you also complete a full charging cycle with a trickle charger?

  21. I read somewhere that short bursts of charge at 18Volts high amperage is a method used by some experts to dissolve lead sulphates… in my experience all these methods either epsom and 18v had never worked, perhaps my epsom concentration is to low, (seems to shorten the life of my batteries) and the 18V leave me only dead batteries, bikes and cars batts all died… perhaps I am doing everything wrong and all these battery methods must be extremely precise to work.

  22. Slight variation. I took all the acid out then washed out the battery with tap water thoroughly. Put hot mixture of Epsom and distilled water in, 1kg salts and 2L distilled water for around 20m shaking the battery a little and put onto charge for a few minutes. Then decided to poor out the salty water and put the old acid back in minus the settled out solids. Charged for 15Hrs then put into car. Cracked over pretty well.

  23. Correct Way Of Reconditioning battery:
    1. Pour out all the OEM electrolyte and save it in a plastic container

    2. Dissolve 250g per Liter Epsom salt in 60°C distilled water

    3. Trickle charge The battery till full. – The Mg2+ ions will reduce (disolve) the Crystalline PbSO4 that is stuck on the plates (Mostly the -ve plates).
    Pure lead (Pb) will be deposited on -ve plate & Lead Peroxide (Pb02) on the +ve plates.
    Electrolyte specific gravity will also rise due for formation of H2SO4 acid.

    4.Now that the plates are clean from the bad kind of electro chemicaly insoluble suphate (Crystalline), Time to now generate the good kind of sulphate on the plates. DISCHARGE BATTERY TO THE LOWEST IT CAN GET.

    5.Drain out the epsom salt solution from the battery. Leaving it there. Interferes with the +ve plates and hinders the evolution of H+ ions necessary for electro chemical action

    6. Put back your OEM eectrolyte( Dont worry if it looks dirty) -The thing is that we must restore battery chemistry to as close to OEM as possible.

    7.Charge the battery with the original acid as eletrolyte.
    You will get maximum 85 % lost cranking power back & add max 50% more life to the battery

      1. This method works everytime!
        Caution though:
        1. Never put Baking soda / Tap water into the battery, It Eats away the Porous (+ve)PbO2 Plate

        2. Never fail to Completly discharge the battery before switching over the Epsom salt solution with the old acid. -Battery Amperage will drastically fall.

        3. If It still cant crank over a cold engine, add some acid when batt is fully charged( use a hydrometer to ensure each cell gets on the scale)

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