Since it was running when this all started I would suspect the Alternator or parts of the Alternator. Depending on the mileage the brushes in the alternator could be worn down to below minimum and need to be replaced. They run about $60 at the dealer and come with a new voltage regulator in one piece unit. It is about at 5 minute fix. They could have been producing just enough voltage to keep the idiot lite from going on but not enough to keep the car running or the battery charged. Before you waste your money on just replacing the battery check out this part. I replaced mine at 200K and there wasn't much left on the brushes. Don't let them sell you a new alternator before you check out the brushes.