Has anyone revived dead Ni-Cad batteries?

[Hawkmoon]

Going through some of my late wife's effects, I came across a battery-powered screwdriver that she had tucked in the back of a drawer in the guest bedroom. It was dead. I left it on the charger overnight, and it's still dead. The charger got warm, but no joy at the tool.

I was able to open it without destroying anything. The battery pack is two 1.2-volt AA Ni-Cad cells, with a connecting strip across one end and the connector for the tool soldered to the other end. So they appear to be standard size and voltage, but not something I can just pop into an external charger.

The charger is marked 6-volts output, but when I tested it I only got 4.7 volts. That should be enough, though, to charge the 2-battery pack, since 2x1.2 = 2.4 volts.

I have no idea how long this thing has been in that drawer. My wife has been gone almost 5 years, and I don't recall ever seeing her use this tool, so let's just say "a long, long time." The cells are probably shorted internally by dendrite crystals. The Internet suggests that I may be able to revive the battery pack if I zap it with 6 volts or 12 volts from a battery charger to dissolve the crystals.

Has anyone tried this? Does it work? What precautions do I need to observe?

[BobR]

I wish I could help you out here but my memory was fuzzed up by chemo. I used to run a battery locker onboard the Forrestal specifically for Ni-Cad batteries. First and foremost they should be completely discharged before attempting to recharge and these sound like they were. They could also be dry, well a lot of them are not sealed so we would use distilled water to replace the electrolyte solution. I have a feeling yours are sealed, and if so are probably past the age of revival. You could try to find some NiMH batteries if you can find compatible one to revive the tool. If you do try to zap them back to life I would say do it outside away from flammables if at all possible. Other than that I got nothing.


bob

[Brad Johnson]

As you've found, no really effective way to revive dead ni-cads that doesn't involve high voltage and a fair amount of current. Considering new cordless screwdrivers can be had for $20-30 I wouldn't bother with trying to revive the batteries. Relegate it to the Big Tool Bin in the Sky and move on.

You could also go with an AA battery-powered cordless scredriver for $12-15 and spring for a NiMH charger with included batteries (about $15 at WalMart). Gives you the option of using the batteries for other devices, too.

Brad

[Ben]

Sometimes it's not the batteries, but the charger. If batteries are completely discharged, some smart chargers won't pick them up. I run into this all the time with spare Nimhs and Nicads I have lying around.

My fix is the paperclip trick. Find a similar battery with a good charge and get two paperclips. Run the paperclips between the batteries, pos to pos, neg to neg for about ten seconds. That should put enough juice in the "dead" batteries for the charger to pick them up. Works about 90% of the time for me.

[Perd Hapley]

I once revived a dead Ni-Cad battery, while at the university in Ingolstadt. That battery destroyed everything I held dear...

[Hawkmoon]

As you've found, no really effective way to revive dead ni-cads that doesn't involve high voltage and a fair amount of current. Considering new cordless screwdrivers can be had for $20-30 I wouldn't bother with trying to revive the batteries. Relegate it to the Big Tool Bin in the Sky and move on.

You could also go with an AA battery-powered cordless scredriver for $12-15 and spring for a NiMH charger with included batteries (about $15 at WalMart). Gives you the option of using the batteries for other devices, too.

Yes, I know new ones are cheap, and I have a couple of others already. I just hate the idea that something with virtually no use has to be thrown away because the batteries got tired. Maybe I'll look for some way to convert it to conventional batteries. If I can make that work, I can use Ni-CAD, NiMH, or Li-Ion.

Maybe the first step is to zap it with an auto battery charger.

[Brad Johnson]

Maybe the first step is to zap it with an auto battery charger.

Set up the camcorder. We need video.

Brad

[RocketMan]

An outfit like BatteriesPlus can build a replacement battery pack for your screwdriver.  I've had them do that for an old Black and Decker cordless drill of mine a couple of times.  An Interstate battery shop can do it, too.
I have even made my own replacement packs a few times by carefully soldering tabs and the old connectors to new cells.

[zxcvbob]

I once revived a dead Ni-Cad battery, while at the university in Ingolstadt. That battery destroyed everything I held dear...

Bravo!    Did you have to look that up, Victor?  Or did you remember where it was?

[230RN]

It's real easy for a battery shop to tab 2 new nicads together for you at quite reasonable prices.  Interstate Batteries in Arvada has done this for me a couple of times for an ancient DeWalt drill I have.

The problem with soldering is that it is real easy to apply too much heat and break the internal connection to the terminal in the battery.  The standard practice is to spot weld those tabs on with a real quick ZOT at several very small spots so that the heat dissipates before it gets into the battery.

I have zapped Nicads many times since I had quite a few portable transmitters, both on the CB bands and the ham bands.  What happens (or at least this is the "lore") is that under constant charging or many charge-recharge cycles, "whiskers" grow between the anode and cathode and short out the cells.  These whiskers can be blasted out of existence by passing a high current through them.

I used to do this with a standard 12V automotive battery on individual 1.2V Nicads, and it involves eye protection and gloves and it's not a good idea to do it under the hood of the car because of possible gasoline vapor ignition.

On the workbench, a very quick connection is made to the NiCad in the proper charging direction by brushing the connection very quickly, maybe twice. It throws sparks and overdoing it will pop the NiCad.  They get fairly warm in this process, and you will never get the same energy capacity as when new, but for extending the useful life for a while, it's OK.

At this point in the brushing and sparking process if you haven't totally ruined the battery, it will show an almost full charge.  Let it cool before putting it in the regular charger.  This also allows the depolarizing agents to recover somewhat from the zapping.

Sometimes this works well, sometimes it doesn't, but pay attention to what you're doing because throwing sparks around on a workbench can be dangerous, too  Use the gloves and the eye protection.  I can take no responsibility for results or possible damages.  I have no information on any possible similar processes for batteries other than NiCads.

You will have a fire extinguisher nearby, won't you?

Terry, hamming it up since 1974-ish, 230RN

[Hawkmoon]

IT'S ALIVE!

And I didn't have to zap it. I opened it up to see about pulling the battery pack for zapping, and I was disappointed to see that there's no plug. The battery pack is hard-wired into the driver. As long as I had it open, I decided to put a voltmeter on it, and it read 2.47 volts. That's not so far off the nominal voltage, so it should do something. Flipping the switch, though, had no effect.

I grabbed the screwdriver tip and tried to rotate it by hand -- no movement. So I locked onto it with a pair of pliers, and with some effort it turned, then rotated freely (or, as freely as an electric motor with no power typically rotates). Flipped the switch, and it spun right up. Flipped the switch the other way, and reverse works.

HAPPY FEET. 

[230RN]

Commutator or brushes are going.

[Perd Hapley]

Bravo!    Did you have to look that up, Victor?  Or did you remember where it was?

I just read the book a couple of months ago, and I still had to look it up.