First and foremost, a disclaimer: NOBODY DO THIS. There that should cover that.
Okay, Here's the backstory: My cordless drill was great for a few years till the batteries tanked out and it turned into an ugly paperweight. After spending my usual too much time on the internet reading about such things I decided I'd juice the crap out of my battery packs with my mig welder to see if that helped.
Initially I did one pack months ago and was so pleased with the result that I saved the other pack to share the experience with you fine folks of the intertubes. You should feel honoured. Or at least less offended than I usually make you.
According to my limited understanding of how the guts of batteries work here is why nicad cells stop working: think of the cell as a bucket of chemical juices with two chunks of metal suspended in it (these connect to the positive and negative terminals). The chemical juices react with the metal chunks and give off magic... or electricity or something. The reason I think they crap out sometimes is because after a lot of this chemical reaction happening a buildup of some byproduct bridges the gap between the metal bits and shorts the sucker out.
Now... that being probably mostly kinda true, here's why the welder helps: My welder on high outputs a little over 30v DC but massive amperage or current. This huge wallop of current blows apart those bridges of crap built up between the internal battery parts and allows the normal chemical reaction to resume in a more appropriate manner. I'm sure there are more qualified people to give proper explanations of this but that's my story and I'm sticking to it.
After seeing a few writings about how to do this trick it seemed like a handful of short, evenly paced zaps was the agreed on methodology so as you'll see in the video I zap the battery in that manner. I arbitrarily decided to zap it 10 or 12 times because that "seemed about right".
Long term testing: As I mentioned before I repaired my other drill pack months ago and it works really well. Not as good as brand new, no, but very usable and much better than doling out the green for new stuff. So that's your lesson in DIY for today.
And now for the sure-to-be award-winning video of the battery zapping event:
