Well, I wish I could relax and enjoy, but today at home without a lot of using it went from 40% to 10% in a couple of hours, and then I put a video and went from 10% to 1% in 5 minutes...
It makes no sense to have a nice iOS if you can barely use it without being plugged. Cmon guys, it's not a TV, it's a PORTABLE device!!!
In a nutshell, consider the law of exponential decay when the battery reaches 50% it's just a limitation of the technology of the time.
I did say that anything below 10% is not guaranteed right?
I also asked for the reported usage stat as listed by the phone (settings > general > usage) please provide that screenshot
Lastly, worst case scenario, backup and erase your phone and start from the ground up with a brand new iOS installation.