How can I change my phone's resolution? I would like to change the resolution of my s4 1080x1920 to 720x1280 not the dpi but the resolution. I have root access and am on android 6.0.1. How can I do this. 

I want to do this to see how much battery I can save. Usually my phone last 3 days (normal use) on my custom 7800mah battery without charing but I don't really have much use for an UHD screen so I want to see if it can last longer by lowering the resolution.
Using adb, no root required
Use the command adb shell wm size 720x1280
Using phone, root required
Download any Terminal app, such as this one.
Type the command su to enter superuser mode, and then type wm size 720x1280 into the terminal.
Source: http://www.theandroidsoul.com/change-screen-resolution-adb-android/