I have this Ryobi 12V NiCad cordless drill that was sitting in a drawer for the past 6 years or so due to dead batteries (2 of them). At least that's what I tought at the time but looking at it more closely this week-end, I could hear a rattle in the charger and could see a slight bump melted in the bottom of the charger.
I opened it up and was amazed at what I found. There is a single small PCB with a barrel connector for the 12V dc adapter, a small resistor for the "Charging" led and a big ceramic resistor for the charging circuit and that's it!!
The PCB was burnt out and cracked in two and the ceramic resistor had fallen off and was rattling in the case. The led was working though, giving the appearance of a working unit.
Now I'm thinking that maybe my batteries are still good, and I only need a new charger.
Would building the one mentioned in the answer here: https://electronics.stackexchange.com/a/21279/11014 work?
Specifically, could I use it to charge all cells in my 12V batteries at the same time?
What resistor values would I use? Maybe there is a faster, safer, cheaper (or all three!) alternative?
Best Answer
Your batteries are gone. Yes, there are some tricks for reviving NiCd batteries, but 6 years is a very long time for a NiCd battery even if it were treated properly and not stored discharged. Even if you "revive" the batteries by blowing the internal dendrites that have most likely formed by now, they will at best hold a small fraction of their rated charge. In practise, they will be useless whether revived or not.
Forgeddaboudit.