I have a Panasonic 24V rotary hammer drill (model EY6813). Recently, one of the stock NiMH batteries began sticking in the charger and the drill. Appears as if one of the battery contacts in "welding" itself the the contact on the drill and the charger. There are marks on the one contact that make it appear as if there may be arcing and the plastic around the contact looks melted, but I don't know how that would happen. Its only occurring on the one contact. I sent the batteries away for a rebuild a couple years ago, but the problem just began. I've stopped using this particular battery, but would like to fix the problem, if possible.

This kind of problem often start in the machines battery contact springs. In the sprigs should be bent or be slack for any reason, poor contact will occur causing heating (as you noticed). This in turn weakens the tension of the spring/contact in the drill itself further. Inspect the contact springs and look for discoloration and moulted plastic around it. You must replace the drills battery contacts to avoid this problem from escalating. The battery may be saved if you gently rub the contact surfaces with an abrasive. Check the charger's contacts although they may not be replaceable so you will have to improvise. Do not use a damaged battery with damaged, misformed, or uneven terminals due to the danger of poor contact and overheating.