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.
Apple designed Apple Watch with a battery life expectancy of 18 hours per day, and from my own experience, I can definitely attest that it usually far exceeds that number. But of course, it all depends on your usage. Depending on what you do with it, you might see better or worse battery life.