Just got an apple watch 7 41mm today. Overall love it. But ive heard that the battery is meant to last 18 hours?

It was 50% when i opened it, and it got to 20% in 6 hours (mind me that it was hardly used. On my wrist and glanced at with always on display.

Honestly that didnt really bug me, however i slapped it on charge until 80% and just saw it go from 70% to 66% in the matter of minutes.

BH is 97%, so it it just the case if watchOS 10 bugs? Will it get better?