What do the app "usage" times in battery settings represent, exactly?

• Percentage of battery used - if you had charged fully and check when the battery is indicating 70 %, i.e., a 30 % drop and it says app xyz used 10% it means that xyz had used 10% of 30% battery expended




• Coming to your main question - it means the total power used by the battery whether in foreground or background , not the time you have used it. For instance, you can check your mail and when you go to another app, mail app goes to background and may continue to sync using battery. Same with chat or any other app which uses sync, scheduled background activities, Wakelocks or other processes. In Android 8.0 (Oreo) , if you tap the app on the battery usage section you will see clearly the actual usage while in active use and while in background as shown

What goes into app usage calculations from a developers perspective

Total_Power_Consumed (mAh) = Bluetooth_mAh + WiFi_mAh + GPS_mAh + CPU_mAh + Sensors_mAh + Modem_mAh+ Wakelock_mAh + Camera_mAh + Flashlight_mAh