Apple Watch Series 8 has a standard “all-day” battery life of 18 hours, where you can text, take calls, and run GPS to your heart’s content. But when you engage the new Low Power Mode ability, Apple Watch Series 8 has an increased lifespan of 36 hours. The bad news is that when Low Power Mode is kicked on, you do end up losing the always-on display and background health monitoring, but you’ll be able to keep track of the time or make any potential emergency phone calls for a much longer period.