It’s Possible To Cut Open A Lead Acid Battery And Restore It, But You Really Shouldn’t

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Finding out you have a dead car battery can be annoying. If you’re lucky, it’s just because you left your lights on, and it’ll come good once you jump start your car and get going again. If you’re unlucky, it’s because it’s worn out and in need of replacement. At that point, most of us would chuck it and get another one.

The alternative is to cut it open and attempt to repair it, which makes a terrible mess and is very bad for you. What kind of person would try to open up a battery? It’s a terrible idea. And yet, in some parts of the world that’s precisely what happens.

This video comes to us from the Facebook page Topspeedgermany, which mostly posts videos that seem to be from not-Germany. In this one, we see a man examining a car battery that externally looks to be in good shape. However, when he tests it—by momentarily short-circuiting it with a fat cable—it appears to be quite dead. If it was charged and working well, you’d expect huge sparks, but nada. Thus, he sets about repairing it in a manner that is incredibly hacky, yet ultimately effective if not safe or remotely recommended.

It goes without saying that you should not try this at home. If you don’t know what you’re doing, you can easily blow up a battery trying any of this stuff. You can also blow up a battery if you do know what you’re doing, but goof up as humans do. This will shower you in burning chemicals and probably disfigure you for life. And that’s before we get into the hazards of lead exposure and the like.

https://www.facebook.com/watch/?v=945839943623264

This video does, however, provide an interesting anatomy lesson on this type of battery and goes to show how these batteries found in most of our cars actually work. Let’s use this as an opportunity to learn about our cars.

A typical “12-volt” car battery is made up of six cells. At nominal voltage, each cell sits around 2.2 volts, for a total voltage of 13.2 volts. In fact, when fully charged, it’s typical to see a car battery sit at 14.4 volts, or roughly 2.4 volts per cell. Conventional wisdom says a lead-acid car battery shouldn’t be discharged below a certain point to avoid damage. If left below 12 volts (2 volts per cell) for an extended period of time, lead sulfate crystals can form on the lead plates in the battery and reduce its capacity and conductivity. Certain charging methods can help reverse this process, but it’s not always a sure thing. Other processes can damage a lead acid battery too, like vibration or physical damage which breaks internal connections or damages plates inside.

Back to the video. With the battery confirmed as a dud, our protagonist peels off the sticker and punches holes in the lid, corresponding to each cell of the battery. In a maintainable battery, you’d normally count six little screw caps for adding water, but this one is a “maintenance-free” battery. Nonetheless, you can still see the spots in the plastic where the service ports would normally go. The holes were probably made to check up and top off the fluid levels inside, but failed to resurrect the battery.

With the holes made, the worker then chisels off the top of the battery in the area of the first cell. He removes the positive terminal of the battery, and pours off the acid of the cell. Repeating the short-circuit test on the remaining five cells, he seems satisfied that it was the cell just removed that was the dud. He proceeds to use a saw blade to cut out the plate assembly of the cell. He then pulls off the pockets that hold the positive plates, dumping out their contents on the ground. As a guide, compare the vision to this diagram of a Varta brand battery of similar construction.

Uk Varta Blue Dynamic

Without going deeply into the chemistry, each cell has positive plates (made of lead oxide) and negative plates (made of pure lead). The positive plates are separated from the negative plates via “pocket” separators. When power is drawn from the battery during discharging, ions are exchanged between the plates and the electrolyte in a series of chemical reactions. These chemical reactions run in the opposite direction during the recharging process. If the plates are damaged or the chemical reactions go too far in one direction or the other—by overcharging or discharging the battery—the cell can fail.

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Thick metal busbar connects the cells. The worker cuts through it to free the plate pack from the damaged cell.
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Removing the plate pack.
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Please never do this.

The worker next cleans out the pocket separators with water, before reloading them with a set of intact positive plates. We don’t see this up close, but the worker appears to be going at the plates with a hacksaw. It’s perhaps likely that they were harvested from another battery and needed to be cut to size.

The plates are then reassembled into a pack with their negative counterparts. Connecting up the plates is done via a rather unique soldering process. A second car battery is used, with a long rod with a tapered tip connected to one of the terminals. This serves as the soldering iron. The other terminal of the battery is connected to a wire, leading to a thick rod of solder. By shorting the “soldering iron” and the solder rod, a great deal of heat is released, melting the solder and making the necessary connections. Hooked up to a car battery that can deliver hundreds of amps provides the huge heat needed to weld the plate pack back together.

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Note that the soldering iron itself isn’t being powered like a heating element and getting hot. Instead, it’s the heat of the arc created by the short circuit that’s melting the solder. That’s why the guy is able to hold on to the “soldering iron’ without burning himself.

With the plate pack reassembled, it’s dropped back into the battery. The same soldering technique is used to reattach it to the battery’s external terminal, and to the bus bar which connects it to the other cells.  Once complete, the battery acid is poured back into the cell.

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Soldering the plate pack to the busbar connection to the adjacent cell. Note the rag stuffed in to protect the plate pack from errant solder.
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Soldering the plate pack to the external terminal. Note the iron ring, used to stop excess solder getting on the sides of the terminal and making it a poor fit.
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Refilling the cell with acid.

From there, it’s a simple matter of sealing up the battery. This is done with a series of sharpened metal rods that are placed in a fire. Glowing hot, they’re used to plastic weld the battery back together. It takes some work, with scrap plastic fed in to fill the larger gaps and holes.

Finally, we see the battery dropped into a Volkswagen, where it successfully starts a wheezy-sounding engine. It was a lot of work, but it got the job done.

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Sticker’s back on, it’s good as new! Well, not really.
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Job’s a good ‘un.

In case we weren’t already clear on this: You should never perform the battery resurrection process depicted above for a bunch of reasons. For a start, it makes no economic sense unless securing a replacement battery is completely impossible where you are. A repair like this takes hours, and in this case, was probably only successful because the first cell was the damaged one. Imagine the carnage if the fix required cutting out one of the middle cells, or more of them!

Beyond that, it’s horrific for the environment and for the individual doing the work. We see acid spilled everywhere, for a start, as well as the plates dumped straight on the ground. You don’t want either on your skin—both because of the burn risk and the potential exposure to lead.

Finally, it’s just not a very effective repair. When you cut apart a battery like this and solder the connections back together, it’s unlikely to conduct as well as it did when it was new from the factory. All those soldered connections are likely of far higher resistance. They’re also comparatively brittle and more likely to fail. Similarly, you need to hope your plastic welding job is good lest you end up with sulfuric acid leaking all over your engine bay.

If your car battery has a dead cell, don’t cut it open. Just drop it off for recycling wherever you bought it and get yourself a new one. Oh, and don’t even think about getting your chainsaw out. You’ll just make things worse.

I will admit to having done my own repairs on lead-acid batteries, but in a comparatively safe fashion. I used to build electric scooters using lead-acid batteries, and my poor engineering choices saw the batteries solid-mounted to an unsuspended scooter chassis rolling on hard rubber wheels. Vibration would cause the busbars to snap inside the cells. I would at times carefully open the top of a battery to make repairs. Ultimately it was pointless, as the batteries would just fail again in short order. At the very least, though, I wasn’t removing plates or pouring out electrolytes. I avoided making a mess and making anyone sick. In any case, I wouldn’t do it again.

Hopefully, this article has taught you a bit about how a lead acid battery works, and at the same time, why you shouldn’t bother to attempt fixing one. Stay safe out there, and keep your blood lead levels as low as possible!

Image credits: Topspeedgermany via Facebook Screenshot, Varta

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64 thoughts on “It’s Possible To Cut Open A Lead Acid Battery And Restore It, But You Really Shouldn’t”

  1. I dont know whether to be impressed or terrified. Top marks for the arc soldering device.
    I’ve seen quite a few such videos.Always from the subcontinent and always involving jaw dropping levels of chutzpah.
    Random alloy turned into gear pump cases,old crankshafts turning into smaller shafts.Ship steel turned into pretty much anything.It’s staggering what they’ll attempt.
    All of it done on dirt floors,in sandals ,with home built furnaces and -if they’re lucky- 80 year old lathes.

  3. I have seen people cutting open batteries but it was an article in Practical Classics about a battery restoration specialist in the UK who did period correct batteries for classic cars. He also operated in full compliance with UK Health and Safety

  5. Back in the day batteries had cells. And you could open them from the top. Mostly you just added pure water. But you could also add acid to refresh the battery. This was accomplished with a plastic lid covering 3 of 6 cells. If I recall at no time was a chainsaw used or required.

  6. At nominal voltage, each cell sits around 2.2 volts, for a total voltage of 13.2 volts. In fact, when fully charged, it’s typical to see a car battery sit at 14.4 volts, or roughly 2.4 volts per cell.

    I’m not sure where you got these numbers. 13.2 is a float charge voltage, you’ll never see that in a standalone battery (lead acid, anyway). 14.4 is a fast-charging voltage and you definitely won’t see that out of your car battery by itself. Generally speaking, 12.6 or 12.7 volts is considered fully charged for 12V lead acid.

    Also, isn’t the process being used here basically arc welding? I guess there’s some overlap between that and soldering, but given that an electrical arc is what is used to fuse the material here I feel like that’s the more appropriate term.

  7. This guy is an absolute hero genius legend in my book. Yeah sure, don’t try this in your first world home, but if you’re in the shit, you want this guy on your team. Simply incredible.

      1. Growing up, we had a bottle of mercury in the basement. We used to play around with it in our hands all the time. One day one of us dropped the bottle and it shattered on our basement floor. I used a broom and dustpan to clean it up. I’m pretty sure I should be dead or have three heads. Where was I going with this story…?

          1. Burning plastic models indoors, sniffing glue, playing with heavy metals, paraquat pot, kerosene lamps for fun, countless breaths of VOCs, and so on. I’m honestly not sure how I’m still alive.

          2. It was pure mercury. My dad was a scientist.

            No shit, we also had boxes of monkey brains in jars. After my parents divorced and my dad had abandoned said brains, we smashed some on the pavement. Mmmmmm, formaldehyde and monkey brains. What a lovely odor.

            1. Decades ago we had a mining geologist in our department who for years had a large specimen of cinnabar ore on his desk that was copiously weeping droplets of mercury, much like this one:

              https://www.minerals.net/thumbnail.aspx?image=MineralImages/mercury-almaden-spain.jpg&size=500

              We’re still not entirely sure what effect it may have had on him but it did encourage most people to avoid lingering in his office for extended periods. One popular theory is that this is why he kept it.

            2. I used to work at a company with a giant abandoned freezer full of diseased fecal samples. Nobody was willing to clear it out so it just sat there, year after year…

              I found that anecdote great for breaking the ice with young children at parties.

        2. As kids we had a kit that included an electric lead melter (basically a souped up hot plate), an open top steel crucible on a long handle, and casting forms to make toy lead soldiers. Yep, elementary school kids playing with molten metal. To this day, I remember that lead smell on our hands. And people still wax nostalgic for the “good old days.” Lol.

  8. I learned a lot from this, though now I’m even more curious what happens when I “recycle” a battery. Does it get shipped off to a third world country, separated into pieces and melted, or just drained and dumped in the ocean?

    1. A friend of mine is a former racecar driver and does custom metal fabrication. One of his regular jobs is to work on a giant crucible at a battery recycling facility that melts the lead from old batteries.

  10. Once again proving that third world denizens are both smart and resourceful. You might think it is dumb to do this but you also would not have a clue how to do it.

  11. I am both horrified and impressed.

    This reminded me of a video I once saw of a guy in Cuba making brake pads in a small garage. Just working with fistfuls of asbestos like it’s no big deal.

  12. See this has to do with the local economy, I know that to an average American it doesn’t make any economic sense, but I lived in a place where you have to pay a full month’s wage to buy a replacement, so this made a whole lot of sense, and people are still doing it today, I know it’s unfortunate, and they definitely pay with their health.

  19. The scars on that man’s arm are enough warning to prevent me from ever messing with a car battery. I hope he at least uses some sort of eye protection. Safety squints aren’t adequate for a job like this.

  21. Fun related fact: many motorcycle batteries are still basically early 1980s tech – not sealed. They come empty, you have to mix the acid/water, open it and fill it, etc. So they’re translucent, you can see most of the plates, etc. inside them.

    1. The translucence of the housing does make it easy to see when the plates have become sulfated. 😐

      The last traditional 6V battery I bought (~3 years ago) came with a container of acid that was pre-mixed: all I had to do was fill the cells, rather than futz about with the ratio, which was nice.

      Modern batteries are a bad idea for older bikes: their charging systems were designed for lead-acid batteries and they may overcharge when connected to lithium or similar. No bueno.

      1. I’ve been using the same model YUSA lead-acid for years on my old Suzuki as I’d heard similar. I’ve gotten better about periodically taking it out to check the fluid levels!

          1. I have a silly little light + screwdriver combo that I keep in my bike’s spartan storage area so I can both get my battery out and be able to see how it looks internally.

            (I also use it when I peer into my tank to be sure it’s not getting rusty…damn you ethanol!)

  23. As you can’t really buy 6V car batteries anywhere, I once made one for an old VW Beetle by cutting a 12V regular one in half with a hack saw. Drained the cut cell first of course. Worked just fine for years, but looked very hacky..

    Battery acid isn’t like alien movie acid, so just wash your hands as quickly as possible if you get any on you, and you’ll live to tell the tale.

    1. I used to work in a moody electroplating factory when I was at Uni. Acid splashes we’re common and several times a week I’d use an emergency eye bath. If I knew then what I know now I’d have bought myself some safety gear and reported the guy to HSE, but it was a quid an hour and I was poor.

      Anyway, after six week of this I was absolutely fine. But they guy who ran the place was a mess. He looked like he was falling to pieces. The whole place got shut down less than a year later.

        1. When you were lowering parts in to the vats on the crane any hollow parts would burp up bubbles and splash the solutions around. If I got splashed in the face I’d walk along the wall with my eyes shut until I got to the eye bath, then I’d wash out my eyes. We filled up the eye bath using the same hose we used to top up the tanks, not sterile water.

          No safety guards, no shields, no eye protection, no labels on the tanks.

          We did shitty quality work too, black anodising came out dark purple so we’d spray oil on it to make it look darker and shiny, chrome plating with fingerprints in it. We also phosphated race car suspension for a local manufacturer, that was the cool part of the job.

          The previous year I’d worked in a tiny factory round the corner on unguarded printing presses and chopping up finger sized bits of card on a power guillotine. I got paid 50p a hour there. Inflation adjusted that’s a tenth of our current legal minimum wage in the UK.

          I’m amazed I still have all my fingers and eyes.

    2. I’ve been unlucky enough to feel the effects of 18M sulfuric acid on my wrist (battery acid is 4M). Just a few drops but that was PLENTY!

      You can’t just wash it off, you need to neutralize it with a saturated solution of baking soda to completely nullify it

      – former organic chem lab TA

      1. Yes, there’s stronger stuff around than battery acid.. My parents used to strip paint off doors, outside in the summertime, every time they moved house, with some home mixed witch brew, because fashion dictated raw wooden doors in the 80ies.

        The regular super marked chlorine used for cleaning bathrooms also takes your skin off quicker than battery acid 🙁

        1. I dunno if I’ve seen super marked bathroom cleaner but I have worked with pool chlorine. That’s 10% vs laundry bleach at 2.7% or less. Strong stuff. It also makes big clouds of greenish yellow chlorine gas when mixed with pool acid.

          Fun thing about chlorine is it decomposes into salt water and oxygen gas if you let it sit too long.

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