I know Apple has a habit of under rating the performance of its products especially for water resistance on the products, but when Apple unveiled the AW Series 2, they said the battery life was unchanged and still around 18 hours. My original Apple Watch I charged nightly and sometimes could go a day and a half off a charge but not often, but my new Series 2, I can go 2 full days without charging and have done so a few times even when using a sleep tracking app all night, I still wake up at over 60% after wearing it the day before.