[mpj76]

Does the battery seem to die all of a sudden or gradually. You can check by periodically looking at the headlights. If it dies gradually, maybe there's a short somewhere. If it dies all of a sudden, try shaking the battery a little and the wiring around it. I had a similar problem and it turned out to be that the wiring looked OK on the outside, but was corroded on the inside. It would be better or worse at times depending on very slight movements of the system. Sometimes it would turn over sluggishly or not at all. Sometimes the voltage needle would dip every time the turn signal flashed. I'm assuming you put a volt meter on the "dead" battery. Did you check the current coming out of the alternator? Keep in mind that the current output at idle probably isn't near the advertised max output. Perhaps the alternator is outputting just enough current to keep the car running, but not to charge the battery?