One possible explanation is (if you were using a Futaba 127 receiver and not using a Futaba connector on the battery lead) that you plugged the battery into the receiver with the connections reversed. This would not be possible with a Futaba connector as it has a flange on the plug which prevents improper insertion. On the Model 127 receiver the center pin (the positive lead) is shorted to the inner pin (the signal lead) on the receivers printed circuit. Now if you plug in a generic plug the wrong way into the battery slot (no keyed flange on the connector) you put a dead short on the battery. If you found melted insulation on the battery leads, this is probably what happened. I do not know if other model Futaba receivers have this problem or not as I've only checked it out on the 127's. I'd be interested if this checks out for you.