Following an update, it typically takes a few charge cycles for the battery to model consumption and predict remaining charge. Your battery performance should continue to improve as you charge it a few times.

If you have other bizarre behaviors though, you might eventually have to perform a Factory Data Reset after backing up pictures, music and videos, email settings, other downloaded files that are important to you.

I have an uncle who got a Samsung S4 and had NO ISSUES during the update. I had issues on my LG G2, and I had to perform an FDR. Not everyone has to. For others here, I've read even after performing an FDR, their device operation was not restored properly. I suppose this can happen.