I gave Easy DPI Changer a try and wow does it make a difference! I just started playing games on here and it's actually playable with the resolution you suggested. Thanks for the advice manThat is quite normal. Perhaps battery guru let you charge only to 80%, thats why restarting it makes 100% coz the app doesnt want your battery to wear many cycle as it might get the battery health tear. Also its pretty normal on the phone to spend its normal charging speed around 80% of an automaticaly.. It's as well to use your phone around 85 or even 90%. Don't let the battery reach 20% underneath. But I suggest you change the phone's default resolution and dpi to 720x1280 - 290dpi if you get the root. (Easy DPI Changer)
IT WILL MAKE YOUR PHONE MORE SMOOTH WHILE BROWSING ALSO GET A PERFORMANCE BOOST ON GAMES WHILE SACRIFICING TEXTURE AND ALSO MINIMIZES THE CPU USAGE BY REDUCING ITS PIXELS, COOLER TEMP.
You can still play in 1080 p on any streaming platform with this resolution.
About Battery Guru
You'd better uninstall it coz its a waste. All battery saver or health checker whatever are always running in the backround all the time. Just make sure you dont let your battery reach 20% and below.