I have no clue. We haven't had ours for two weeks, yet, but nice pummeled the poor thing so much that I don't know if it's fair to say it lasts x-hours.
I used it constantly yesterday, making calls and playing podcasts, starting at about 7 or 8am. It was just below 40% remaining by about 12:30pm.
I'm guessing that's pretty good, considering I literally mean "constantly," during that time.
On days that I'm working, using it for browsing and audio consistently, but less frequently for calls, starting at 6 or 7am, it tends to have about 35% or so remaining by 6,7, or 8pm.
All of this is with no charging.
128GB iPhone 6 Plus on T-Mobile