I agree. Electrical circuits are composed of a power source and a load. A bad diode in an alternator could cause a short circuit condition to the battery. The battery probably gets slightly warm. The alternator (if the culprit) will likely get warm because the current will be flowing thru at least one of the windings. Hook up an ammeter to the batt terminal. You should never see any current with the engine off. Is the alternator an original Delcotron?