Is there a way to set the phone to sleep automatically?

[AC Question]

my phone won't automatically go to sleep anymore? And because of this, it dies quickly.

 

[Rukbat]

It's not the phone that's not sleeping, it's an app that's waking it. If the battery stats don't show which app, try Wakelock Detector. You have to know which app it is that's causing the problem, so you can freeze, uninstall or reinstall it.