Seriously.
Yes, seriously. While battery does degrade over time.
A lot of people don't realize how often they "touch" and activate their screens which are the most common reasons why battery drains. I gave her my 5S (sold her 5S a couple of weeks ago) since she thought her 5S battery was bad.
I get a good 6 or 7 hours of "heavy use" plus standby time. That's "heavy use". So I know my battery will last from 6am-5pm most days.
My wife is still getting the same 6 or 7 hours of real time use. But her phone is dead by 3pm. It's cause she on it texting, facebooking etc.
Real time use is the most important aspect of figuring out battery life. None of this overall time from off charger. Since standby time can vary so much.
Just look at Samsung's deceptive advertising about it's low battery mode. What they don't say is you can't even touch your Samsung Android phone to get those battery life results. It's not rocket science here with battery. I can leave my iPhone alone for 24 hours and it will barely drain 5% when almost all the radios are shut down and nothing is activating the notification.
Heck I went away for one week and left iPad air on. I came back 7 days and iPad air battery life was still 93% after 7 days. Crazy. And it was on. The wifi model