5 days after 3-year anniversary dealer check-up and warranty expiration date, car wouldn't crank. Towed to dealer. Dealer replaced battery and tested charging system; said A-OK. 5 miles from dealer after picking up car, battery light came on. Returned to dealer. Dealer now says alternator has failed. Dealer replaces failed alternator. Did the failed alternator cause the battery to fail, or did the failed battery cause the alternator to fail???