While an autopsy, undertaken the same day Presley died, was still in progress, Memphis medical examiner Dr. Jerry Francisco announced that the immediate cause of death was cardiac arrest. Asked if drugs were involved, he declared that drugs played no role in Presley's death.
Power Reserve notification (left), Charging the Apple Watch (middle and right). As for charge times, Apple says it takes about 1.5 hours to reach 80% and up to 2.5 hours for a full 100% charge. Real-world Watch battery performance.
As others have stated, standard return is 15 days. You do also get the standard 1 year warranty on the Watch and you can get AppleCare if you so desire. If it is a good Best Buy you should not have too many problems returning it if that's what you choose.