Many, many years ago, I obtained for myself a Ryobi Craftline 3.6V Handy Tool Kit. This tool kit comprised of a handle which contained 3 Nicad batteries in series, giving 3.6 Volts, and a very simple charging circuit. The charging circuit was very simple, a series resistor to limit the current. This worked for many years, and over the years needed replacement of the batteries since they die after a while.
You might think, ok – I should be able to get better equipment now, surely? The tool kit had a number of heads that could be attached to the handle, a torch, drill, screwdriver and last but not least a soldering iron. I don’t think there is anything like it now. Certainly the torch, screwdriver and drill is available but no soldering iron. Anyway, the batteries had died some time ago and I hadn’t felt the need to buy expensive Nickel Cadmium cells to make the battery pack.
Just a few days ago, while sorting out the years of accumulation that happens in any man-cave, I came across a number of Canon NB-150 batteries, still new in box. I don’t know if anyone remembers the old Canon BJ-10e bubble jet printer. It was very common, and was one of the first bubble jet printers produced by Canon, preceded only by the BJ-5. It can be upgraded with a sheet feeder which I had, and also by adding a battery, the NB-150 – it would be a portable printer. Quite handy if you felt the need to do some work at the beach, but that is another story.
Ok, the Canon NB-150 batteries – I had bought some during an auction, those many years ago, and I had used a couple and still had a number of them left. I had a look on eBay, and sure enough, someone is still selling them. New in box, they sell for around US$10 however I doubt that they are working after so long a period of time. I took one apart, then connected my battery charger/exerciser to it to check which cells are working.
Here is a photo of the box, an intact battery and the one I took apart. In this one, only the right-hand three cells were working, the others were shorted. Nickel cadmium batteries after a period of non-use grow whiskers which short out the battery eventually. One way to fix those is to burn them out, by putting a high current through them. I remember in my previous laboratory days, I would connect a cell to a power supply and put 10 Amps through it, at a low voltage of course. There was a current limited variable power supply that could supply up to 30 Amps – I just had to increase the current until the short circuit disappeared. Or if you are unlucky, until the cell explodes – but that never happened for me since I am generally very careful.
Now, it so happens that I only need three cells, which meant that the working cells that are joined together are just right to fix my Ryobi. That is what I did, cut those working cells out and installed into the handle of the Ryobi, now I have a working handy tool kit again!