To sum up.
The iPhone 6 Plus has no problems with battery life.
No matter how you use your phone at least have 8/9 hours of screen time.
This is more than enough for any human being.
Who has an iphone 6 Plus and think a bad battery, I would advise looking for something to do
Go see a movie, read a book, run, work kkkk
Seriously, The Plus is a monster in battery