Aluminium Sulfate Lead Acid Battery Conversion




quick how to on aluminum sulfate electrolyte for lead acid batteries.

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Purchase Ingredients.

you will need aluminium sulfate, a hydrometer, distilled water and a two buckets.

also you will need a face mask. long sleeves, safety goggles and water on hand.

this job could cause death or serious harm from explosions and acid spills.

you will also need a battery charger, applicator bulb and common sense.

Step 2: Drill Holes Into Vent Caps or Remove Caps.

if you have a sla battery you will need to drill into the plastic.

use a pneumatic drill a regular drill could cause sparking or explosions.

you have two choices.
1.fully flatten the battery to sulfate the plates. this will produce a super saturated acid.

2. fully charge the battery. check with hydrometer that the electrolyte is 12.5 to 13.00. this indicates 80 to 100% charge.

Step 3: Create Saturated Aluminum Sulfate Solution.

you will need room temperature distilled water. add aluminium sulfate slowly to water while stiring. check with hydrometer.
it takes a long time but you should be able to get a reading of 12.5 or more specific gravity easily.

if you heat the water or add too much the aluminum sulfate will precipitate when the electrolyte cools.

Step 4: Tip Out the Acid From Battery.

pour out acid from the battery into a large bucket. be carefull not to spill any on yourself.

Step 5: Add Electrolyte

add aluminium sulfate solution to each cell. use a bulb designed for this purpose. about 5 bucks from auto store.

feel free to use any ratio. I have found 20% sulfuric acid to aluminium sulfate works the best.

100% tends to precipitate and provide low cca.

Step 6: Charging

you will need to charge the battery to 16.8v. this electrolyte solution doesnt off gas as much as battery acid.

gassing starts at 14.7v and gets rapid at 15v plus.

I use a turnigy charge set to 7 cell mode. it will cut out at 17.1v. but the battery only reaches 16.8v so you need to turn it off manually.

Step 7: Testing and Final Thoughts

I have mixed results. all my batteries were dead or used batteries and performed less than originally specified.

for example 710cca produces 540 hca. this battery is 90ah and 160 rc. I got 60 mins rc.

only notable improvement is less heat produced and less off gassing.

you can't buy sulfuric acid in Australia now but you can still buy aluminium sulfate which works ok.

pic shows resting voltage and cca rating of two batteries of the same make and capacity.

one is pure aluminium sulfate. the other has 150ml of battery acid added per cell (100ml of aluminum sulfate solution at 12.75 sg in each cell).

the latter has higher cca and lower resting voltage. the former has higher resting voltage and lower cca.

batteries converted with 20% to 60% sulfuric acid added seem to produce about the same CCA and about 80% the Ah capacity. not magical results but note worthy.

a resting converted battery that is flat will still read 12v. but when loaded will drop instantly. specific gravity only changed by 50 to 80 points between fully charged and flat. also sulfation doesnt appear on plates as dramatically as with battery acid.

I would appreciate real professional testing of this electrolyte. it is hard to produce meaningful analysis with the junk I am using.

try it out and post your results.

Be the First to Share


    • Made with Math Contest

      Made with Math Contest
    • Multi-Discipline Contest

      Multi-Discipline Contest
    • CNC Contest

      CNC Contest

    22 Discussions


    1 year ago

    I dont think the Aluminium Sulphate sold as pool FLOC is the correct Alum for this process, I have Aluminium Ammonium Sulphate on order from IHERB and believe it to be the correct one for this process but it seems hard to get. I got impatient waiting and tried the Aluminium Sulphate sold at bunnings as pool floc but this has yeilded a battery considerably weaker than required however it has not been cycled to build it up yet so it might get a bit strong. Resting voltage after conversion is 10.7V, it was 13.2V prior to conversion. Its Cranking amps has been quartered. The ammonia part also seems to be the alkaline component, Pool floc is a very strong acid. Pool floc works but go for the Aluminium Ammonium Sulphate if you can get it, its what John B used from my research.


    Question 1 year ago on Introduction

    Can a similar process work with an AGM battery, either used or new (no electrolyte added)?


    5 years ago on Introduction

    In step 5 I see:
    "feel free to use any ratio. I have found 20% sulfuric acid to aluminium sulfate works the best."

    1) there should be NO sulfuric acid; lead alum is an Alkiline battery, not an acid battery
    2) "any ratio" often in chemistry, a very specific ratio is required. This may be the cause of your results. One source says 10% alum to distilled water, by weight; and NO sulfuric acid.

    4 replies

    Reply 1 year ago

    Al2(SO4)3 is acidic, Pb is amphoteric. How can this be an alkaline battery? Added H2SO4 should reduce the voltage of each cell since it dilutes the Al2(SO4)3 electrolyte. Expect to dissolve 30-35g Al2(SO4)3 per 100mL H2O for saturation.


    Reply 1 year ago

    Besides, alkaline batteries aren't rechargeable unless special chemistry is used.


    Reply 5 years ago

    try it and see how it goes. im no longer interested in this subject. I figured the sponge lead fatigue was the major cause of failure. nothing you can do to put the powder back on the plate so why bother?

    its like trying to put rust back on your car and hope it turns to steel.

    my experiments were riddled with holes but actually doing it debunked it sufficiently for me. if you think there is more to it I wish you the best.


    3 years ago

    According to what I have been reading, you dont need to add any sulphuric acid. Just use the alum and water.

    3 replies

    Reply 1 year ago

    "Alum" is not used here, and has no specific formula.


    Reply 1 year ago

    @Steinzel have you had a success using only Aluminium Sulfate ?


    Reply 1 year ago

    I'm not experimenting with this tech, I'm only reading about it.


    2 years ago

    I have made several of these Alum batteries and use a inverter to plug in a lamp during power outages. Depending on how bad your battery is sulfated they work well, holds 11 volts for hours


    3 years ago

    well after going through this , hubby would need a 6x4 shed the other end of the block . As for my phone battery and laptop battery that wouldn't hold a charge I wrapped it in plastic and put it in the freezer for a day then fully recharged it been good as gold since freezer wipes the memory so it takes a full charge

    1 reply

    Reply 3 years ago

    Im looking into if there is any fact or logic in this considering there is not such thing as Li-ion batteries having ANY kind of memory whatsoever, there are different control factors at play here


    3 years ago

    How can you trust someone who doesn't even know how to rotate a pic...

    1 reply

    Reply 3 years ago

    hahah beat that turned the laptop


    3 years ago

    very goog tips