3 days? wow!
Mine lasts all day (from 6:30am to 10pm), and there is a good 10%/15% left. And I am constantly listening to music, watching youtube videos, doing work, facebooking, playing chess and such. Seriously a big step up from my 5S.
To be honest, I don't use the phone for video, wordprocessing work and facebook (which I hate). Mostly calls, sms, internet, camera shots (photos).