In addition to the new Screen Time statistics in iOS 12, Apple has enhanced the battery section in Settings to chart your battery level and usage time. You can also see when your device was put to charge, for how long, and how the battery level changed while charging.
You can view your battery level and usage for the past 24 hours or the past few days. Battery usage is broken down by app and can be viewed as a percentage or time.
Apple provides totals for 'Avg. Screen On Usage' and 'Avg. Screen Off Usage'. Developers can check out the new Battery menu from the Settings app.