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

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.

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.

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.

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.

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.

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.

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