The chart also shows you when the device was on charge (look for the lightning icon on the battery level chart).
You can use this information to diagnose battery drain issues. Here are some things you can use this information for:
– An app going berserk in the background will show lots of activity in the background compared to screen activity (try disabling background activity for that app and see if that helps).
– It can spot charging problems (was the battery actually charging when you thought it was?).
– It can be used to spot poor battery performance (look for battery charge falling rapidly).
– The breakdown of activity over time, both over a day and over several days, is very welcomed, and will no doubt become my go-to tool for diagnosing battery drain issues.