Revive Nicad Batteries by Zapping With a Welder




About: Tim Anderson is the author of the "Heirloom Technology" column in Make Magazine. He is co-founder of, manufacturers of "3D Printer" output devices. His detailed drawings of traditional Pacific...
Nicad batteries often die in such a way that they won't take a charge and have zero voltage. This usually means they're shorted out by crystal dendrite growth.

Here's a method of bringing them back to life by zapping those shorted crystal dendrites away with too much current and/or voltage. We'll use a welder as a power source. You could also use a car battery, a DC powersupply, or almost anything with some voltage. Charged-up capacitors are popular for this because you can get a very fast pulse out of them and still limit the power. it's a lot safer that way. Speaking of which,

If you get killed by a poisonous explosion it means you did something wrong.
Electrocution is a real possibility also.
Ask your parents how to not electrocute yourself with a welder.

If your tool has a non-battery problem, here's how to fix that.

Watch the video and see how zapping is done.
Excellent stills and video shot by Fungusamungus
Excellent Video editing by Noahw

Step 1: Gather Your Materials

You'll need:

Dead Nicad batteries
Nicad battery charger
Voltage source - we'll use a welder
insulated gloves
safety goggles

Step 2: Check Your Battery

Charge your battery up for a few hours or overnight to make sure it's charged.
If you suspect your charger isn't working you can trickle-charge it from a different voltage source.
To make sure you don't overcharge it put some little lightbulbs from christmas lights in series so the current is below 1 amp. I use 1/2 amp usually.

When you're sure your battery has had a fair chance to charge, check the voltage with your multimeter. Since you're reading this, the voltage is probably a lot lower than the label says it should be.

To see how much current your battery can put out, run the drill. Grab the chuck and stall it to get a feel for how much power it has.
That way you can compare the "before" to the "after" and see which is better.
Science depends on rigorous methods like these.

Step 3: Check Your Welder

Use your multimeter to make sure your welder is supplying DC and whether the gun or the clamp is positive and negative. Welders are sometimes AC and sometimes the polarity is backwards.

Turn the knobs to see what voltage range the welder puts out when no current is flowing.
This one puts out about thirty volts at the max setting.

Step 4: Zap the Hell Out of the Frickin' Battery!!

The title says it all.
Tap the positive end of your welder to the "plus" terminal of your battery
while holding the negative end to the battery's "minus" terminal.

You should see some sparks and nothing should get welded to anything.
No welding please. If you get killed by a poisonous explosion it means you did something wrong.
It should feel like something good is happening.

Step 5: Try Out the Battery and See If It Worked

Try out your battery. It ought to be much better almost immediately.

Step 6: Zapping Individual Cells

Pete Lynn dropped this battery pack in salt water. It shorted out the cells and it has been fully dead for a year or so. We peeled it apart to get at the individual cells. We scraped the salty cardboard off them and zapped them with a car battery. After that it worked fine.
It's easier to zap an individual cell than the whole pack at once.
Sometimes you can't revive a cell. You can cut or unsolder it from the others and replace it with a good one.

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    193 Discussions


    3 years ago

    would this work for lithium ion 18 volt Ridgid battery. I have both nicad and lithium 18 volt batteries for my rigid tools and I got the regular battery working and am trying to get the lithium ion working. I've been reading a little about possibly changing the 18 650 batteries. any suggestions or help would be greatly appreciated.

    4 replies
    Maxim GridinPilot_diver

    Reply 3 months ago

    I'm really sorry if you will don’t understand much from the video. I just did not prepare videos for foreign viewing. (Yes, and I do not speak English perfectly, so as not to be ashamed) I simply laid out the results of my hobby in my native language.
    In short, under certain conditions, zapping can be successfully and safely applied to lithium-ion cells, including the restoration of batteries for screwdrivers, laptops, electric vacuum cleaners, etc. For the restorations must be the original Sony cells, LG, Samsung, Sanyo / Panasonic. Chinese cells die usually completely.
    To repair, I use a homemade spot welding, using a 12 volt car battery and a magnetic current interrupter (or plate with Power MOSFETS). The number of pulses is usually 20-100, and the duration is 10-20 ms. It is important to choose a number and duration so that the battery cell does not heat up above 40°C.



    Restoration of separate Li-ion cells (0.7volts) with tests and measurements of parameters of capacity, current, etc.

    If you are interested, ask here or there - I will tell everything that I know myself.

    Reply 3 years ago

    yeah don't zap Lithium ions ever - you can check out you tube videos of guys exploding Li-ion cells by pumping household AC into them from a distance to convince yourself!

    bowen93's suggestion is good. usually these batteries fail because the first cell of five (or double/parallel-wired twin cell) gets discharged to zero or even negative voltage. This happens usually after very long periods of storage and is due to that first cell(s) being used to power the battery protection circuit gets run down way below its minimum failure voltage of about 2.7 volts.

    While it is convenient to design this way (with 3.7 volts nominal at that first cell being perfect to power a standard 3.3 volt micro controller-like circuit), this is a major design flaw found in most of the first generation packs and only a few manufacturers have moved away from this design I believe.

    So open up your pack and see if only a few cells are killed and replace those. I usually cannibalize other afflicted packs for their good cells but you can use salvaged laptop 18650 cells in a pinch. They aren't rated for the same high current but will work fine for less heavy duty tools like drills especially if you don't run them too hard or long, without taking breaks to let them recover from the strain.

    Make sure to test all the cells as sometimes random cells will die too, for reasons I can't explain. Remember that for a 10 cell battery, which is really 5 twin/parallel cells wired in series, the cells die in pairs typically.

    good luck , and be safe working on those -- esp be very careful, whatever you do , to not short out the raw cells w solder wire or metal work surface or tools etc - as they produce massive instant current and bad burns and/or battery core meltdown can result!


    Reply 3 years ago

    i agree with Pa1963 dont try it with lithium ion, you can however change the individual cells with li-ion or even get that cell working again, i have managed to get a few cells working again by plugging them into my small li-ion charger i bought from ebay, as it supports protected and unprotected cells, only use this due to my turnigy didnt allow me to put a small boost into the protection to start it back up so the battery would charge again, but if you do that to prevent it from happening again try fitting a small balance charging circuit to the battery case


    1 year ago

    I was skeptical about this when I first saw it, but shortly afterward my wife reported that our Bissell Perfect Sweeper wasn't taking a charge anymore after using it several years. So I figured out how to open it up and took out the 7.2V NiCd battery pack.

    I have an old laptop power brick that puts out 19.5V at 6.5A, which sounded like a good zapper. So I jumpered it to the battery pack for a couple of minutes of Zap time, then tried charging it on the regular charger. Sure enough it took a charge and now runs fine. We'll keep an eye on it to see long it stays good.

    Thanks for the inspiration!


    3 years ago

    This only gets the battery pack working for a while then the dendrites grow more and short it out again. By then the real capacity of the cell is pretty low. Your charger may say it 's done but that only means the charger has stopped, NOT that the cell now has the full charge capacity that it used to.

    If you are in an emergency and need the tool to work badly then it's worth a shot but if not, you gained very little making the effort to zap the battery and would be as well off putting the effort into finding a good price on a replacement pack or an entire new tool if you're in the mood for an upgrade.

    I just tried zapping two Rigid 18volt batteries that had no voltage and would not charge. One stopped working last summer and the other one died over the winter. They are both working now and have fully charged. Thanks for the tip.....

    1 reply

    Reply 3 years ago

    I think you mean they have stopped charging, not that they are fully charged. They won't be remotely close to their rated capacity once they have degraded to this point.


    4 years ago

    Works without welder. In a USA standard 110v AC outlet (white wire = neutral and black wire = hot), you can touch neutral wire to negative DC terminal and hot wire to positive DC terminal. Give a quick pop and the battery is like new.

    2 replies

    Reply 3 years ago

    Though technically this is a valid method for this purpose, since you only need a quick tap on the battery leads, keep in mind that all you're doing to get DC from the AC outlet is using ground and hot instead of negative and hot, so from the 60Hz +/- cycle you're basically getting 60Hz +/0 instead of true DC.


    Reply 3 years ago

    What? No. Ground potential is supposed to be as near neutral as possible so you're still getting AC not DC using earth and hot. It's just a bad idea all around and potentially dangerous too, which makes no sense at all when there are so so many other safer options.

    Kids, DON'T DO THIS !!


    3 years ago

    I just used a similar method to this on a small scale to revive a couple dead NiMH AA Batteries. I don't have a welder but I used a 24V DC wall adapter used to recharge the NiCd cells in a handheld vacuum in my college dorm, and it only took a couple zaps to get the 1.2V cells to take a charge again. I was also able to use that adapter to get some 7.2V packs working, but for that I basically just kept them wired together in parallel with my multimeter until it read 8V, at which point my battery charger stopped refusing to finish up filling them.


    4 years ago on Introduction

    Hi, just wanted to thank you Tim and all others so much - I took a 12v car battery charger and put it on the 12V cordless battery and zapped it up to 75 Amps cycled it a couple of time. Then I selected 12V at 2 amps and let it sit for a bit and now the battery runs better than the one that didn't have any problems and maintains a full charge. thanks so much again!


    5 years ago on Introduction

    Awesome project! Also, try using a battery desulfator :D


    6 years ago on Introduction

    This also works with a 1 fard capacitor. Also can use 1 fard capaciator for welding the battery tabs.


    7 years ago on Introduction

    my father inlaw has 2 electric bicycles , both with dead nicad batterypacs

    I will try this trick to save him 600 euros for new batterypacs.....



    7 years ago on Introduction

    Folks, the only thing I can add is that some batteries have small circuits internally (e.g. Laptop/Ham Radio/ VHF-UHF) and if you exceed that circuits voltage or current you may Zap the whole battery pack into orbit. Just be careful. As an example, My DELL laptop battery has a series of LED's that indicate the amount of rmaining charge so I'm very certain it has a built in circuit, in this case, disassem bly and individual cell restoration would be recommended.