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.
While we don't have any clues to its exact running time, Tim Cook's statements about charging the device at night suggests we could be looking at up to one day of use for the device. We'll have more information about the Apple Watch's battery life as it becomes available.