Should I charge the phone 40% to 90% like the internet is saying? Or should I always go for full charge from 0 to 100%?
I wouldn't say 40% to 90% is written in stone, but you definitely shouldn't let it drop to 0 and you shouldn't let it plugged once it hits 100%.
The phone will stop charing battery once it hits 100%, no need to worry about unplugging after it hits 100%. The proof, let your phone charge during the night and touch your charger when you wake up in the morning to see it is cold.
It looks like you're new here. If you want to get involved, click one of these buttons!