Doesnt look like it was cjarged to 100%. Twitter is possibly not letting the phone sleep too. Social media apps can kill a phone. Maybe disable notifications for it and see where that takes you. Or get rid of it.
Screen and Android OS are basically are your phone. So any changes to those core systems will drastically slow your phone down, or make it unusable.
Android System is comprised of a huge list of programs, usually system applications. Pressing in Android System will show you just how many different programs are included in that percentage. (And, unless you know what you're doing, messing / disabling those apps can actually cause your phone to become unusable)
Screens are usually the biggest power hogs on phones. Turn on automatic brightness, turn off Always On Display, lower your screen timeout, and Enable Keep Screen Turned Off.