Recondition A dead battery?

B

BrainPain

Joined
Feb 26, 2026
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I'm looking for tutorials or guides to recondition auto batteries and any advice from anyone that has tried it.
I'm thinking about emptying one and replacing the acid and distilled water. I have read a couple of pages on the web and watched a YouTube video or two So I wonder if anyone has had any good luck doing it with a dead battery.


Thank you
 
The acid isn't what 'wears out' inside a lead acid battery. Over time it converts into a sulfation product and coats the plates. You need to get the sulfation off the plates in order to have a good result and the easiest way to do that is recycle the whole shooting match into a new battery including melting the lead down and recasting the plates.

Reconditioning a Lead Acid battery is at best just an experiment. I would never trust one to work long term.
 
BrainPain said:
I'm looking for tutorials or guides to recondition auto batteries and any advice from anyone that has tried it.
I'm thinking about emptying one and replacing the acid and distilled water. I have read a couple of pages on the web and watched a YouTube video or two So I wonder if anyone has had any good luck doing it with a dead battery.


Thank you
Click to expand...
Check youtube on methods for desulfating a battery. That is your best bet going down this rabbit hole. I have had decent results using a Battery Minder that continously desulfates, but it takes several weeks, plugging it in every evening when I return home. (its a slow process). The youtubers use a welder. Good luck and don't hurt youself.
 
Batteries are not that expensive in the grand scheme of things. Just replace it. Then you eliminate, (or greatly reduce) the chances of It stranding you somewhere, or quit when you need it the most.

Not to mention there is always risk messing around with acid and heavy metals that produce hydrogen gas...... Which is about as explosive as you can get.
 
I've tried it and failed on several batteries in the past few years with a fancy dewalt charger, but i didnt ever go through the 'add water' step.
 
For flooded lead acid batteries, the only method I've used that worked was to use a welder.

For AGM batteries that are not too far gone, deplete slowly to 10V, charge with Constant Current at 1/10th the 1C rate for 16 hours. Make sure to set the power supply voltage up to at least 22V. It won't go that high, but it will go to 17 or 18V.

Note: The 1C rate is often not published for AGM batteries, but is about 60% of the C20 rate. The standard rating for most batteries.

AGM example: 30AH rating C20. A 1C rate would be 60% of that. Or 18AH. Charge that battery at a constant current of 1.8A for 16 hours.
A true premium AGM like Odyssey would be 70%, or 21AH. So charge that battery at 2.1A for 16Hours.
 
cptbarkey said:
I've tried it and failed on several batteries in the past few years with a fancy dewalt charger, but i didnt ever go through the 'add water' step.
Click to expand...
It's hit or miss on motorcycle batteries. I've done it for some where it tends to overcharge a bit more than it should (and you should be checking lead acid batteries on a motorcycle every so often as part of maintenance anyways). Once you're at the point of adding water they seem to drop of exponentially. Might get you through a season but just plan on replacing it.

I've heard of the desulfators working in some instances, but as one poster mentioned here it takes a few weeks. Seems not worth the effort unless its $$$ for the battery and you want to see if you can stretch it.

I know it appears on the surface that it's mostly a waste of time, but if funds are low and you just want to get through a season or for a bit longer until you can afford the new battery it could be helpful. One thing my dad does is go to junkyards and pull batteries out of wrecked cars that came in recently and with no more than 3 years old.
 
Yes, gloves. I think that this is the first video that has shown one of those guys using any kind of safety equipment.
 
This is what I have found from some extensive research and some trial & error myself - it may or may not work for you.

I have only finished up to step 9 myself and recovered batteries that had less then 15 mΩ resistance to like "new", and any batteries that tested bad at the point, I personally decided that I was not going to proceed with the remaining steps (to me it wasn't going to be worth the effort as I am really good at finding batteries on deals).

Flooded Lead Acid Batteries ONLY
  1. Completely Clean the battery & terminals.
  2. Test the battery using a Battery Tester and record the result.
    1. Good Battery - just charge on Battery Charger/Tender
      1. CCA are within 80% of original rating
      2. Resistance is less than 5 milliohms
    2. Bad Battery - charge on Battery Charger/Tender & retest with Battery Tester
      1. CCA are less than 80% of original rating
      2. Resistance is more than 5 milliohms
  3. Open Battery Vent Covers
    1. Ensure fluid level is above lead plates, if not add distilled water ONLY
  4. Use a good quality Battery Charger/Tender that can desulfate and even start charging a completely dead battery (Example: Noco Genius)
  5. After the Battery Charger/Tender indicates the battery is fully charged, then proceed to use a Battery Tester to verify and record the results.
  6. If the battery tests good then you are done, if the battery tests bad, then proceed to step-7.
  7. Use a sticker welder (or a compatible charger) at very high Amps (100) for 5 cycles.
    1. Welder Charging Cycle - monitor battery temperature
      1. 5 minute charge
      2. 20 minute cooldown
  8. After the 5th cycle is completed, use a Battery Tester to verify and record the results.
  9. If the battery tests good then you are done, if the battery tests bad, then proceed to step-10.
  10. Empty out the battery acid into a clean container.
    1. Don't throw it away, as it can be reused.
      1. Use multiple coffee filters to filter the used battery acid.
  11. Prepare epsom salt mixture
    1. Mix epsom salt in distilled water and heat up the solution until the salt is fully dissolved
  12. Fill up the empty battery with the salt mixture.
  13. Repeat step-7.
  14. After the 5th cycle is completed, empty out the salt mixture, and flush with tap water until clear liquid comes out of the battery.
    1. Close the battery vent covers and shake the battery for a minute or two before dumping out the water.
  15. Rinse/flush the battery with distilled water.
    1. Close the battery vent covers and shake the battery for a minute or two before dumping out the water.
  16. Refill the battery with filtered or new battery acid to the correct level.
  17. Recharge the battery to full.
    1. retest to see if the battery tests good or bad, record results.
 
Even the cheapo battery chargers these days have a Desulfate / Regenerate function. I wouldn’t expect miracles but might give you a tiny bit of extra life from a ‘dead’ battery.
 
zzyzzx said:
Recondition A dead battery?
You are most likely wasting your time.
Click to expand...
Yes.

Hopefully Brain Pain will come back and read some of the responses that actually make sense here. There are existing threads on this topic, some from similar first-time members, but I don't feel like linking them.
 
I've never had much luck trying to rejuvenate dead batteries. Won the lottery once and managed to resurrect a very dead lawn tractor battery that needed to sit on the charger for a few days before it got any appreciable charging current, yet somehow I got a couple more seasons out of it. Otherwise, I've had very little success. Even tried the de-sulfate mode on the charger but no joy.
 
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