So that out of the way try this.
1. Uninstall apps you don't use daily.
2. Pull up the screen where it shows all apps running. Close them all by tapping the X on the app or if your phone has a close all, use that.
Apps sitting in the background can eat power.
I am the owner of a Xiaomi Redmi Note 4 for about a year now. The phone has a 4100mah battery so it should last for at least a day.
Earlier (months ago) it was easy to get more than a day of juice with one charge, but recently my phone always dies at around 6pm already.
Is this because my battery is just not as it was before, or is it because of an issue that maybe can be fixed? How can I check this?