I have 1 DeWALT 18 volt NiCd batteries. One charges without incident. If I attempt to charge the other, a whining noise is emitted from the battery or charger. Is it safe to attempt to charge this battery?
It's possible that the battery's days are numbered, but I doubt that the whine you're hearing comes from the battery itself. That noise is called "coil whine" and comes from the windings of the transformer(s) inside the charger.
An electrical engineer (which I am NOT) could probably explain why you get the noise with one battery and not the other; I can only speculate that the charger is having to crank up the voltage a bit to force a charge into that one. If that's the case, it could mean that the battery is on its way out, but in any case I wouldn't worry that it's going to blow up.
charging one now that whines intermittently on a battery that is trying to go bad. my dewalt charger has "automatic tune up" which is supposed to pulse your battery to help keep it working longer. maybe that is the whine i hear.... so i'm charging this for an hour see if it holds a charge or not. if not i'll probably look up how to replace the batteries inside it. right now it's blinking at the correct rate showing it is charging.