I found a 18v Craftsman "Professional" recip saw at the dump. Nice condition, but I knew that the battery was bad. That's why it was at the dump, right? I knew better than to take it, but I couldn't help myself :-)
At home I put the battery on the charger and, sure enough, I got the "Defective battery" light. A voltmeter said zero. I opened up the battery, to see if maybe it was just one or two cells that were bad. In the course of dicking around with it, I tried charging it with a variac-bridge. When it took some charge I put it back on its own charger & it charged! It has held the charge at full voltage for a few days now & runs the saw very nicely. I guess that the problem was that it had been run down all the way & the charger couldn't handle that.
Also, when it was charging, I put an ammeter in the circuit. It charged at 3a with a 75% duty cycle (on for 15sec, then off for 5sec). Anybody know why?
Bob