My Nexus 5 sometimes drains from 100% chage to zero overnight. This only happens occasionally, and I am assuming some of the apps is not properly handing Android wakelock preventing phone from going to sleep. This assumption is confirmed by the following screenshot (Android KitKat 4.4.4). It shows 9 hrs of "keep awake" time and only 19 minutes of "CPU total" time. Question: how to find out what app is holding that wake lock preventing the phon