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February 23, 2009 3:47 PM   Subscribe

I have sulfuric acid, de-ionized water, and basic lab equipment. Can I revive my crappy car battery?

My battery holds very little charge. A couple of days ago, I left the radio on in my driveway for about one minute and the car wouldn't start when I got back. If I let it sit for more than a few days, it's iffy whether it will start.

Is there anything I can do, like drain out all the fluids and put in a new sulfuric acid solution? Or should I just purchase a new battery?

Also, don't worry about giving me safety advice. I know how scary H2SO4 is, but I'm a broke student and could do without spending ~$100 on a battery!
posted by scose to Travel & Transportation (18 answers total) 1 user marked this as a favorite
My understanding of battery failure is that when a battery is fully drained of charge, it's the battery plates that physically degrade. Clean water and fresh acid will not help with that.

That said, all I know about lead-acid batteries I read on random web pages, and I do know that the plates are made of sturdier stuff in some models (glass mat in some, cardboard!?! in others).
posted by zippy at 3:56 PM on February 23, 2009

I'd pay $100 to avoid the possibility of chemical burns, lead poisoning, and a crappy battery that I will have to replace in a month anyway.

And what zippy said about the degradation of the lead plates.
posted by 517 at 4:03 PM on February 23, 2009 [3 favorites]

If you're a broke student, can you afford the medical bills that might result from cracking open and monkeying with a car battery full of hazardous chemicals?

Purchase a new battery.
posted by pdb at 4:04 PM on February 23, 2009 [2 favorites]

FWIW, I just replaced a battery at Autozone and paid about $70 after the core allowance.

Car batteries, as said, don't take deep discharging very well. This I've learned after replacing several batteries in the past, thanks in no small part to children who enjoy Climbing Into Things almost as much as they enjoy Pushing All The Buttons.
posted by jquinby at 4:07 PM on February 23, 2009

I'd be worried about doing this too well and a) creating a battery with a higher voltage output that harms some other part of your car, b) creating a battery that explodes and/or leaks acid or c) both.

Sometimes batteries just take a dump on you. I'd just replace it, and/or turn it into a real science experiment, and take it out of the car, hook it up to a volt meter, etc, etc.
posted by Cool Papa Bell at 4:07 PM on February 23, 2009

Yup, it won't work. The plates will be saturated with PbSO4, which would be stupid to try to clean off.
posted by 517 at 4:13 PM on February 23, 2009

Response by poster: OK, you are all probably right... I guess I was hoping there was some secret revival technique that the battery manufacturers don't want us to know about, but it looks like battery death is more or less final.
posted by scose at 4:13 PM on February 23, 2009

Yep, it's the plates that are the problem, most likely.
posted by Green Eyed Monster at 4:20 PM on February 23, 2009

Best answer: Depends. As mentioned above, the plates in deep-cycle batteries tend to become sulphated*, leading to reduced capacity - and more so in car batteries, where the plates are not pure lead, but usually lead alloyed with antimony or similar to provide strength.

Most car batteries, though, tend to fail physically - the plates crack, break away from the grouping bar, get shorted by loose residue, etc. If they fail because of an internal (partial) short circuit due to residue build-up it is possible to wash them out and re-fill them, but usually not worth the effort (because that residue is material that has been lost from the plates anyway).

(* FWIW, it can in certain cases - large (1000's of A/H capacity) backup supplies in telco applications where the cost of replacement is high being one - be worth going to the trouble of 'de-sulphating' cells / batteries. But it's usually only a short-term measure, and you almost never get back full capacity.)
posted by Pinback at 5:36 PM on February 23, 2009

Pinback is correct. The basic answer is no. The acid bath isn't what fails, it's the lead plates.

More specifically, the lead plates are more like thin lead sheets, since the more surface area there is on the lead, the more amps the thing can put out. So the lead is very thin. In addition to that, there are other things that happen besides just acid and water.

Adding onto that, as the lead and acid interact over time, the lead doesn't reform exactly in the same malleable structure it started out as. It gets brittle and the failures mentioned occur.
posted by gjc at 5:51 PM on February 23, 2009

For one, you don't have to worry about making "too much voltage"...the reaction has a specific voltage, times six cells.

But yeah, get a freakin' battery. The plates are toast. It happens more in winter, where there's more drain on the battery to turn over an engin full of more viscous oil, then you leave teh blower on...*cough*...anyway, once a dead battery is good and frozen - even a newish battery that just has been drained - it's good and dead.
posted by notsnot at 7:39 PM on February 23, 2009

For one, you don't have to worry about making "too much voltage"...the reaction has a specific voltage, times six cells.

What happens with a different acid solution? Wouldn't a lower ph solution than the standard create more electrons with a shorter overall battery lifespan?
posted by Cool Papa Bell at 8:18 PM on February 23, 2009

Wouldn't a lower ph solution than the standard create more electrons

More electrons means more current, basically. I suppose it might reduce the internal resistance, which would have the effect of a slightly higher voltage in practice, but that isn't what you are talking about. Check out the wiki.

Of course I don't know much of anything about electrochemistry, so I might be missing something.
posted by Chuckles at 8:59 PM on February 23, 2009

Reports vary on whether trying to desulphate a sulphated battery is at all worthwhile or not. There are various circuits you can find on the net (e.g.) which claim to be able to restore some capacity to a sulphated battery.

Sulphation is a different failure mechanism from having the plates physically degrade, though. Not much you can do if your plates are falling apart. I've heard that sometimes a battery will fail because, as the plates degrade, sludge builds up at the bottom of the battery and shorts out a cell or two; removing this sludge could possibly restore the battery. I think that's a pretty long shot though and how you would physically do that on a modern battery I don't know.

You could perhaps just trickle-charge the battery so it's not as much of an issue that it doesn't hold a charge very well.

In any event, you should plan to get a new battery when you can afford it, even if you manage eke out a few more months of use from this one.
posted by hattifattener at 10:35 PM on February 23, 2009

Well, assuming you're going to stick with using this one until you either can afford a replacement or you figure out how to fix it, I would recommend:

Not using the radio (or at least not using it when the engine isn't running)
Turning off the overhead light so you can't accidentally leave it on
Starting your car every day whether you use it or not

That will at least help keep it from dying on you again. Best of luck!
posted by Slinga at 6:55 AM on February 24, 2009

If you look around there is probably an auto shop that sells used batteries. It won´t be in a nice neighborhood. The battery you buy there won´t be very good, but it will be cheap. Make sure it´s held down properly in the car, as it might be the wrong size.
posted by yohko at 9:30 PM on February 24, 2009

Following up on yohko, you can buy batteries at Pick-n-pull. They're right by the entrance. PnP's exchage policy is generous - if it covers batteries then you're all set (assuming their prices are reasonable - call ahead).
posted by zippy at 1:01 AM on February 25, 2009

Response by poster: Well, just to follow up, the water level in the battery was very low. I filled it up and so far, no jump starts needed. Looks like I've got a little bit more life out of it at least. Also looked up some plans for DIY trickle chargers, and it seems pretty easy to make one from a 12 volt wall wart and a big ol' resistor...
posted by scose at 12:45 AM on March 6, 2009

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