Apple claims that the Apple Watch Series 8 models have a "all-day" 18-hour battery life, which may be enhanced to up to 36 hours with a new Low Power Mode featured in watchOS 9. The bad news is that when you enable Low Power Mode, you will lose the always-on display and background health monitoring, but you will be able to keep track of time and make any potential emergency phone calls for a considerably longer amount of time.
Apple claims "all-day" battery life based on 90 time checks, 90 alerts, 45 minutes of app activity, and a 60-minute exercise with Bluetooth music streaming. Apple assumes four hours of LTE connectivity and 14 hours of iPhone connection for LTE devices. The Apple Watch will drain quicker in certain conditions, such as during phone conversations or exercises.
The Apple Watch Series 8 can be charged quickly with Apple's Magnetic Fast Charger USB-C Cable and a power adapter rated at 18W or higher. After only eight minutes of charging, you can get up to eight hours of sleep tracking.
But it's worth noting that charging time for an Apple Watch is quite fast; if you're using an Apple 20W USB-C Power Adapter, it will take roughly 45 minutes to reach 80 percent and approximately 75 minutes to achieve full charge on Apple Watch Series 8.