Battery drop from 80% to shut down in less 3-4 hours

Bought a new Garmin Venu last week and after a few 'twigling around' with settings and downloaded watchfaces (and twice 2-3 hours total battery time!), i have a stable setting. Factory watchface, once a day sync with iphone, no always time on (short mode) and power off at night. Almost 6 days of battery life, daily from 8 till 23:00. I notice that every time battery lifetime drops fast from 80% to shut down in just 2-4 hours. During these last 2-4 i only wear the watch. Do you have similar experiences?