God awful battery life, any tips?

I charged my phone to 61%, since I was going out in a rush and didn't have time for a full charge.

I got home, just as my phone hit 2%, maybe 3%

I was only gone 3 hours. I didn't watch videos, play any games, and the battery menu said Screen and Android OS were the culprits. I was in a job interview, so it's not as if I was using my phone much during this 3 hour window either. And this was exactly three hours too - 10:16 to 13:16

It seems to have slightly fixed itself. I'm on 10% and have been off charge at least 12 hours, and used the phone moderately throughout the day. No idea what could have caused this though since no new apps have been installed?