Adding sulfuric acid to a car battery?

I accidentally spilled some of the battery acid from my car’s battery when I took it out from the car to fix something that was obscured by the battery. The battery got tipped over and I didnt notice, not until about half of the fluid spilled out. All the cells were affected.

I added water and recharged it, but now the cranking seems weak and the specific gravity is 1.20 instead of what it was before when fully charged, about 1.27.

I was thinking I’d just buy some sulphuric acid and add it until the specific gravity is back to normal.

Is this a good idea? Anybody ever tried this? The battery is good otherwise and only about 18 months old.

The sulfuric acid used in car batteries is very dangerous to handle. If you can find a source, you may get lucky and replenish the battery with it. But, for me, I’d just consider this battery toast and simply replace it. I don’t have the equipment to handle battery acid safely and it is just not worth it to me considering the very dangerous potential for human and property damage.

Some of the shops I dealt with in my youth had batteries delivered dry, and had a special bladder with acid and a spill-proof nozzle designed to fill the battery cells and shut off the flow of acid before removing the nozzle. I haven’t seen anything like that in decades.

1 Like

The battery is done. You can add distilled water to a battery if the level is low because the water evaporates from the acid. But if the battery is spilled where the electrolyte is lost no amount of water will bring the battery back to life.

You could go out and buy a motorcycle or lawn tractor battery where the electrolyte is in a seperate container and add that to the battery. But then you end up with a useless motorcycle/lawn tractor battery.

This is one of the times where you hang your head and learn from the mistake, and then move on.


Call around, you might get lucky. There’s also a product called “Liquid Fire”, which is marketed as a last-ditch drain opener for use when all else fails, but is actually concentrated sulfuric acid. As far as how much to add, I’m no chemist. You might also take it to a battery shop and see if they can help you, as they would have the chemicals and handling equipment, and know how much to add if you’re lucky.

If you do find some acid and choose to do this yourself, make sure you wear wrap around goggles and acid resistant gloves that cover your forearms. It may also be helpful to make a kind of smock from a garbage bag or similar to protect yourself.

Since you can measure specific gravity (many folks don’t even know what that is) it is clear you have sufficient chemistry training and experience to continue with your idea. It ought to work. Don’t give up on it, and let us know of your success.

Not that I recommend it (sealed batteries are best for cars, IMO), but sulfuric acid is readily available at Lowe’s and Home Depot. They both sell marine batteries for use with battery-powered backup sump pump systems. Those are shipped dry and you add the sulfuric acid and water at home. It’s been about 3 years since I last had to buy some, but I want to say it cost around $15-20 for enough to fill a marine battery about the size of most car batteries.

The catch is properly disposing of the excess. It’s hazardous waste, and must be handled properly - which means finding a disposal agency. Here that means saving it until the summer when the county has free drop offs, or paying an agency $50-75 to take it other times of the year.

How old is the battery?

Should you be daring enough, do be careful how you handle it. For instance, if you add water to the acid, it will boil violently. If you have to mix to get to the right specific weigh, carefully add acid to water - not the other way around.
I’d just toss the battery and get a new one. Eyes and skin are not cheap to replace.

Its only 18 months old. Take it in and warranty it. The last I warranted,it only cost me $17 pro rate. That was 4 years on a 6 year warranty.

A real battery store should be able to sell you “Battery Acid” in a one quart or one gallon box. These boxes come with a dispensing hose attached…Handling the acid just takes a little common sense…

But you have another problem…You must dump out all the diluted electrolyte from the battery before you can add the fresh acid…What do you do with THAT?? Nasty stuff to get rid of…Maybe the place that sells you the acid can help…

Some folks have raised the issue of disposal of surplus sulfuric acid, believing it to be a problem. You, George, have enough of a chemistry background to know that small amounts of acid can be neutralized with baking soda or baking powder from your kitchen. Once neutralized, the acid is totally safe in all ways. You can wash your hands with it, or sprinkle it on your tomato plants. A bit of sulfate will do them some good.

Mixing Sodium Bicarbonate with Sulfuric Acid will produce a nasty sludge that’s at least safe to flush down your toilet…

Buying a new battery is looking better all the time…

Yep, whenever I have gotten a lawn mower battery, I always have leftover acid. I just use baking soda to neutralize it. I really think Tester is right though, just get a new battery and move on.

@SteveF: A bit of sulphate may do the plants good, but since it would be LEAD sulphate, I wouldn’t dump it on tomato plants or any plants that you were planning on eating from.

Another source for acid would be used batteries. Not the best choice, but a lot of batteries are junk because of the plates, not the acid. Take your SG meter with you and a container, and of course, plenty of safety gear.

If you have an airport near you that caters to light airplanes, ask a mechanic there if he has any battery acid.
Airplane batteries are shipped dry charged, with the h2s04 in a separate container.

BUT: The instructions for any aviation battery I bought would always say: “Always add water, never add acid” after the battery is put into use.

Spend the money for a new battery. Let the parts place dispose of yours properly.

Lowes sell this product:

Basement Watchdog 6 Quart Battery Acid

It is sulfuric acid and will likely work for you. It’s about $19. I’m sure you won’t need 6 quarts, but sulfuric acid will not degrade over time unless it has something to dissolve.

Safety corner: It makes sense to wear a rubber apron, long sleeves, a face mask, and rubber gloves when handling concentrated acids. Make sure you have a running water hose nearby in case you need to dilute the acid quickly. It can have a nozzle on it, but have it ready to turn on in an instant. And do not pour water into acid. It will create heat much faster than pouring acid into water, and can lead to glass breakage and a big spill. The heat will create dangerous fumes, too. I know that you will not mix water and acid in the battery, but you might use the leftover acid for something else.

Thanks to all for great comments. Safety is paramount, I agree. It seems like it is possible to do it safely by being careful and using common sense by wearing proper safety gear. And I already have some sulphuric acid on hand. But I think the best thing is what most of you say, to take the battery back to where I bought it and see what they’ll give me on the warranty. Will do.

I would not suggest putting the neutralized excess battery acid on vegetables, as it will have a little dissolved lead in it, but Steve is correct that acid is not a problem to dispose of once it is neutralized.