Extending Power Tool Batteries

I think all DIY lovers with a cordless tool know that batteries are a short-lived thing.
And buying a replacement is not so simple. And the point is often not the price (although the price of batteries for a professional tool may not be at all childish), but the fact that it is unrealistic to find the right model.
I myself encountered this problem after two years of operating a professional screwdriver with 18V batteries at 1.5A * h.
Despite the fact that I prudently bought 2 additional batteries in the kit to the two in the kit recently, all 4 began to work indecently little and the question arose. The matter was complicated by the fact that the Italian manufacturer, alas, went bankrupt a couple of years ago. The trademark was sold to the Chinese, and the line of professional tools was discontinued. So the simple decision to “throw out and buy new ones” did not work.
Caution - a lot of photos.

After disassembling the battery, it turned out that:
  • the battery consists of 15 nickel-cadmium (judging by the markings on the battery case) "cans" with a capacity of 1500 mAh connected in series
  • Measurement of voltage on the "banks" showed that out of 15 cans, only two have problems (0.2V and 0.8V, while the remaining 1.1-1.2V is so small because the discharged battery picked it)

Of course, it was possible to simply disassemble one battery into spare parts by restoring 3 workers. But I thought that was not enough. Since it does not eliminate the cause, but the effect.
But the essence of the problem is that neither the battery nor the charger contains the so-called. "Balancer" (as well as the balancing connector). Those who are not in the know will easily google what “battery balancing” is.
In general, I decided to fix the manufacturer’s defect on my own.
What was needed:
  1. The charger is suitable for charging single cells. I searched with a charge current equal to the cell capacity (1.5A) - this is the "passport" mode for this battery, one-hour charge. Of course, it would be even better to immediately find a charger-balancer for 15 NiCd cells - but I did not even try. Not in our city ...
  2. A good soldering iron (40-60W) A lot of power is needed, oddly enough, so as not to overheat the banks when soldering.
  3. Suitable connector. Most of the time it took to search for a suitable connector - in the photo you will understand why ... I came up with a loop from a floppod (yeah, I'm a system administrator and a programmer) By the way, even two connectors come out of one good loop
  4. Every little thing

I will not describe the process in detail - everything is already clear from the photographs.
I note only a few points.
Firstly, safety precautions . Be extremely careful!
Remember, the battery is a rather dangerous thing, because even when discharged it contains residual energy that can cause a fire during short-circuit and rather aggressive chemicals.
With excessive heat with a soldering iron, the bank may well explode, spilling all this chemistry into your face. And I warn you right away - do not even try to do this with lithium batteries !
Secondly - in my case, a gasket is glued to the banks from above and below, as it turned out - mica and very fragile.
Thirdly, inside there is very little space for wiring (which, incidentally, must withstand a current of 1.5A without heating). Worse, the stiffeners that press the cans are quite capable of transferring wiring. So their laying around the ribs was rather dreary. By the way, the photo is not obvious - but the wires in the cable and the connector are connected in pairs (doubled), since the number of pins is more than required. For batteries with a lower charging current, you can bite off the extra part of the connector saving space, and laying wires will be easier.

The process itself:
1. "initial" state of the battery

2. A disassembled battery with cut out "problem" banks (in the end, I left them for now - deciding that they are recoverable and will still serve). Pay attention to the numbering - the banks are located in the battery rather intricately and without numbering in any way.

3.4. Cutouts in the battery case and in the screwdriver’s seat - for the protruding part of the connector (ABS plastic - so melted with a soldering iron tip and the circumference cut off with a knife)

5. Lid with an inserted ribbon cable (fitting)

6. Cans with soldered balancing connector already assembled back

7. Charging an already assembled battery. So, yes, 15 hours - because one bank each. But this needs to be done once out of 5 or 10, in other cases, regular charging of the entire battery. However, you can charge the “regular" and then recharge the "problem" banks - which will be much faster. By the way, the problem that has not yet been resolved is also visible here. This charger only works with a pair of batteries. I have not yet figured out how it works and just stuck the “left” battery in the second slot. Do not try to charge several cans of one battery at once in such a “multi-socket” charger! Remember, they are connected inside the battery! And from 18 volts on its contacts, the charger can tell you everything that it thinks about you. Loudly.

I hope this article helps someone extend the life of the battery. And ecology is good, and the wallet. And most importantly - there is something to occupy your hands and head.
Good luck

Upd: I reloaded pictures on habrastorage.
Upd 2 - Part Two

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