Introduction: How to Revive Old Lead Acid Batteries

Picture of How to Revive Old Lead Acid Batteries

If you are like me you probably have old lead acid batteries sitting somewhere probably discharged

If you dont use lead acid battery always charge it before and recharge it every 3 monts

I ve tried this method on maintenance free lead acid, sealed lead acid and lead acid batteries , only difference is that maintenance free and SLA have hidden caps

Step 1: You Will Need

Picture of You Will Need


-Adjustable PSU or Taper Charger (Smart chargers wont work)

-Dead battery

-Distilled water (you can also use rain water)

-Rubber gloves




-Super Glue

-Paper towel


Step 2: Measure Battery Voltage

Picture of Measure Battery Voltage

Connect multimeter to your battery and check voltage

Your battery shoudnt be lower than 11.8v (30%) in open circuit

If you read lower than that you will need to revive it if its higher than that try to just charge it

100% = 12.73 v
90% = 12.62 v

80% = 12.50 v

70% = 12.37 v

60% = 12.24 v

50% = 12.10 v

40% = 11.96 v

30% = 11.81v

20% = 11.66 v

10% = 11.51v

Step 3: Inspect the Cells

Picture of Inspect the Cells

Place paper towels on your working areas

Now if you have SLA or maintenance free battery you will need to remove lid with screwdriver

Put on gloves and remove caps

Do this in well ventilated area

Wipe any wet spots with a paper towel

Then look inside cells and you should see white fabric that is dry

If you see brown fabric with white lumps your battery is probably sulfated and your chance of reviving battery is really bad

Step 4: Add Water

Picture of Add Water

Take a syringe and fill each cell with water and look if fabric is absorbing water

Slowly shake battery and let it rest for 10 minutes

Step 5: Turn on Your PSU

Picture of Turn on Your PSU

Now you will need to connect your multimeter to show you how much battery is drawing

Set your multimeter to 10A and connect it in series with charger and battery

When you connect it to the battery an it should draw 100-200mA

Thats sign of dead battery

Set your psu to 14v or connect your charger and let it sit for day or two

After that your battery should draw 500-1000mA

Then just leave battery and calculate how long battery should charge

Ah capacity = Amps that your battery is drawing x hours

For my battery 8Ah = 0.39A x 20,5 h

Step 6: Testing Battery

Picture of Testing Battery

Now leave your battery for 1h and hook it up on car hadlight or any 12v bulb

Voltage of battery shoudnt drop lower than 12v


Mjtrinihobby (author)2016-05-20

I know you put a lot of passion and effort into this project. I commend you on this. However when lead acid batteries fail, regardless of the variant, they simply cannot be revived and expected to produce even 40% of their original capacity. They are truly disposable after failure. Also, do not interfere with lead acid battery insides; you don't want to risk your future with lead poisoning (it can happen easier than you think). Be safe and keep up the great work!

tutdude98 (author)Mjtrinihobby2016-05-20

I revived few lead acid but they usually die after 5-6 months and then you cant revive them
Also they cant deliver same amperage as they used to

Mjtrinihobby (author)tutdude982016-05-20

I abandoned Lead Acid technology about 3 years ago. I use exclusively the Lithium Iron Phosphate chemistry for my home solar bank, my car engine and also all my portable power sources. Environmentally safe, safest Lithium chemistry in production, low self discharge and far longer service life. I love LiFePO4 with a passion!

mad_b (author)Mjtrinihobby2017-12-08

Hi. Does this change to use LiFePO4 requires some change on charger or it works the same as original lead acid alternator/rectifiers in the car?

Mjtrinihobby (author)mad_b2017-12-10

Fully compatible with OEM alternators.

Agelosp (author)Mjtrinihobby2017-12-06

can you convert a car battery to that ?

tutdude98 (author)Mjtrinihobby2016-05-20

I started using 18650 becouse you can make packs how you like
If you need less voltage or more, maybe more capacity

symetrixit (author)Mjtrinihobby2016-11-24

Mjtrinihobby - I totally agree with you. Besides lead poisoning you just forgot about sulfuric acid - not a lemonade ;) When discharged electrolyte decompose and adding water won't revive the battery. Adding acid is better but still won't do the miracles. Lead sulfate crystals deposits on the battery plates and damage them reducing active surface. There is now way that you can bring the battery to brand new condition at home. You will be lucky if will work at all. Sadly sites like this :

use people lack of knowledge and combine it with playing with their emotions (eg. We had to spend the last dollar on the battery and leave kids hungry) and steal their time and money while making them risk injury - so more costs and time as well, and something that they can't buy at all - health.

RickL49 (author)2016-02-21

Keeping the battery full of water is part of the maintenance it shouldn't be low. If you have to add water you haven't been taking proper care of it.

tutdude98 (author)RickL492016-02-23

Yeah but SLA should be "maintenance free" becouse they have hidden caps and you dont need to add water

ChristianS145 (author)tutdude982017-09-25

The only way Sealed Lead Acid batteries can loose fluid is by over charging when pressure inside needs to exhaust, those caps are in fact one way valves. A pulse charging can clean the plates, and restore plate surface .

tutdude98 (author)ChristianS1452017-09-26

I had several SLA batteries that were not charged and sitting in garage, they were all somehow empty.

Never tried pulse charging or desulfation but i noticed that "dumb" charger with only transformer and rectifier works better when restoring old batteries.

Auxleman (author)2017-09-08

very interesting, I will be trying one based on your instructions. We have oldecided lead acid batteries lying around. Thanks.

amiir (author)2017-03-08

hey guys. i have 12V SLA battery and it wasn't use 1 years. after
charging its not save power as it should. the voltage was 3.6V and it
dies after 10Sec. i collect some rain water and clean it with cotton
filter. refill the 6 cells and charge the battery for 5H. in first hour
it takes 0.3 ~ 0.9A and in next hours 2.6Amps. is it normal? what was my
mistake? the voltage is 7.78 now and its not die fast. it can provide
7.78V for a LED lamp almost 3hours. what should i do to make it 12V or
near 12?

tutdude98 (author)amiir2017-03-10

What capacity is your battery? 2.6A should be normal (if its more than 7ah, 2.6A is fine), charge it till it reaches around 12,6v

amiir (author)tutdude982017-03-14

hey tutdude98. thanks for answering me.
that battery was died. i have another one. 12V 1.4AH Maintenance-free sealed lead-acid and dry. i fill
the cells with rain water. wait for 24 hours. and charge it with 15V. in
first minutes it takes just 0.1A (100mA) from power supply. but in 3
hours it reached to 2.15A. when it was on 2.15A it seems like boiling
water inside of battery and rubber caps jump from cells and make a bad
smell. after charging i use the battery with 12V 2A Car Lamp and it make
it glow perfectly. voltage was 11.08.

this is how the voltage get down.

4:15PM : 11.08

4:35PM : 9.09

4:45PM : 6.58

and finally after 24Hours its get down to 0.0Volt.

i cant understand this battery!

any help would be appreciated.

thanks again for answering my comment.

tutdude98 (author)amiir2017-03-14

Sounds like you have shorted cell, or one really bad cell
Also, if you charge 1.4Ah battery with 2A, it should take less than 1h to charge it and you should disconnect when water starts to boil
Keep in mind that after you revive the battery it should lost part of its capacity ,1.4Ah battery might drop under 1Ah so you might not be able to draw 2A from it longer than half hour

tutdude98 (author)2017-02-24

"I.m.S1Victor351a month ago

That EZ battery reconditioning site is a ploy for money....notice how the OP could easily describe what he supposedly did (that would actually be helpful) but he doesn't, he just refers you to a site that asks you for MONEY before telling you how to do it. Stick with sites like this and youtube."

Gaia Slut (author)2017-01-06

can anyone confirm this actually works? i mean im sure theres a way to do this just i find this topic confusing as i never thought this was possible

tutdude98 (author)Gaia Slut2017-02-22

i tried on few batteries and it worked, but they didnt have back their original capacity, they would lose something like 30-40%

aquascapist (author)2017-01-22

Don't forget to wear goggles. I have a SLA I can't wait to try this on. Thanks.

I.m.S1 (author)2017-01-16

That EZ battery reconditioning site is a ploy for money....notice how the OP could easily describe what he supposedly did (that would actually be helpful) but he doesn't, he just refers you to a site that asks you for MONEY before telling you how to do it. Stick with sites like instructables and youtube. They're free

vazz_v (author)2015-12-12

super thank you for the well explanation. But pls help me determine the charging time. Also tell me what will happen if the battery is overcharged.

tutdude98 (author)vazz_v2015-12-12

Look at your Ah rating
Then divide it with current (A) that you are charging it with
If you have 10Ah battery and current is 1A it will take 10h to charge the battery

When the battery is fully charged , water inside will start to boil and release gas

symetrixit (author)tutdude982016-11-24

tutdude98 - One correction, the water does not boil in the battery. Overcharging causes electrolysis of water and decomposition to oxygen and hydrogen.

tutdude98 (author)symetrixit2016-11-26

Thanks for correction

lmlisak (author)2015-12-05

I also buillt a desulfator from

... to see if it helps... It seems to take a week to get some benefit.

I do everything you do. I am charging between 14.5 and 14.75 with constant voltage PSU... then take it down to 13.5 to float.

We have a scrapper in town that gets APC units in every two weeks, and I get a lot of 7Ah and 17Ah to play around with.

thanks for your article..

symetrixit (author)lmlisak2016-11-24

Imlisak - there are no scientifically confirmed methods to reverse sulfation besides one - buy a new battery and recycle the old one.

vazz_v (author)2015-12-12

thank you for your reply. I will post my result soon...

AndyNguyen164 (author)2015-05-29

This is awesome but could you please explain the step 5 where you connect the battery to the multimeter and charger to check drawing current? Also what is a PSU or taper charger?

Sorry for the dumb questions. Thanks

duckee25 (author)AndyNguyen1642015-10-06

PSU is nothing but the supply unit box present in your computer's CPU and I too dont know what is taper charger.Sorry for that.

tutdude98 (author)AndyNguyen1642015-06-05

Instead of motor you connect to psu or charger
PSU is a Power Supply Unit - converts mains AC to low-voltage regulated DC power that you can use to power motors, bulbs, leds or charge batteries if voltages match
Taper charger is a crude unregulated constant voltage source and most of the time its just a box with transformer and diodes to convert high ac to low voltage dc to charge batteries

pfred2 (author)2014-08-19

That looks like a Jar Jar Binks battery to me. Yuasa need to buy a new one!

jmoody14 (author)2014-08-19

This is awesome and very well explained. Will be trying this on my campervan batteries this weekend!

BLR_RAVI (author)2014-08-19

very nice...this kind of battery is very common in homes emergency lights..i will try too.nice project

seamster (author)2014-08-19

Very handy, thank you for sharing this!

About This Instructable




Bio: My name is Alen and i study electronic engineering. I love to make anything that needs electricity, hack and mod things as well building anything ... More »
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