Reviving NI-Cad Batteries

[billwmeyer]

I found this link on another forum:

http://www.instructables.com/id/Revi...-with-a-Welder

I was very sceptical, and worried about a battery blowing up in my face. I had 2 dead very old 9.6 volt batteries for my Makita cordless drill. I do not own a welder, but it was said on the forum that jumper cables off of a car battery would do the same thing. I have a jump starter that I used to spark the batteries. One is perfect, the other is about half power. I may try to spark it again.

DO THIS AT YOUR OWN RISK!!

I couldn't believe this battery that hadn't even been on a charger for months, because I gave up on it works so well after a charge. I have used it to drive about 30 screws so far and drill a few pilot holes, and it is still going strong.

Bill

[leehljp]

I am going to give this a try. I have a PC 14.4 with two batteries that are all but dead. I haven't used it in almost a year. I also have a Japanese Ryobi 12V with one almost dead and one that is at 50%.

[billwmeyer]

Hank,
I hope it works for you as well as it did for me. I was really surprized.
Bill

[Jim Frye]

The fix may be temorary...

I agree that the voltage pulse will most likely break down any crystal build up that has formed in a cell and is blocking current flow. It may be a quick fix to enable you to use the pack in a bind. However, it will not prevent new ones from forming in that aged cell and I would expect the pack to fail again in the not too distant future. Also, if the pack is "dead" from other malady (open cell or shorted cell), your results could be spectacular. If you use this suggested method, please take all safety precautions to protect yourself. I have never had a resussitated pack last very long. My experience is that rebuilding or replacement are the only long term fixes for a dead pack.

[pelligrini]

I've had similar results like Jim describes. I didn't have access to a welder, so I used a battery charger on start. I did get a little more life from one pack, but it wasn't all that long, maybe a month. The other pack I tried it on did improve, but ever so slightly. It would barely hold a charge for more than a few days. That was an improvement over the less than one day. These were two old 9.5v B&D packs from my first cordless drill. I ended up getting some higher capacity replacement packs off of ebay.

[LCHIEN]

There's some sense in doing that. A frequent cause of failure of battery cells in a pack is shorting out due to dendrite growth - very thin metal strips that plate their way across cells.

Pulsing a lot of current thru the cell will, like a fuse, burn out these dendrites. And put some charge on the cells. One secret is simply pulsing it like he does which limits the total amount of energy transfered to the cell, just enough to run the drill for a few seconds and not enough to overcharge and explode the cells which might happen if you hold a large amperage, high voltage source across the pack for a while.

If you have an 18 or 19.2V pack, then a car battery will not do the trick - not enough voltage to drive current into the last few cells that come alive... you will need more volts than the pack nominal voltage. Just how much is sort of a function of the how high the source impedance is (internal resistance - for a lead acid cell this is usually low - good). In general for a car battery charger or a lead acid car battery, you'll probably want 6-10V more than the nominal battery pack voltage. Two car batteries in series for a 19.2V pack is barely adequate.

As jim says, this may be a temporary fix, if the cell has a tendency to grow dendrites because its old then it may only last a short time. But it could work several times.

OTOH, if the battery pack is no good to you then trying this is not exactly risking a lot.

As a safety measure, wear saftey goggles/glasses and even zap the bettery behind a safety shield if possible.

[sparkeyjames]

Or just do the safe thing and have your old packs rebuilt. My Sears Craftsman Professional drill driver has 12v packs both died of crystal growth. I took them to Batteries Plus and they were rebuilt for about $25 each. Good as new.