https://arstechnica.com/gadgets/2018/08/p-is-for-power-how-google-tests-tracks-and-improves-android-battery-life/

With the last version of the Android P Developer Preview released, we're quickly heading towards the final build of another major Android version. And for Android P—aka version 9.0—battery life is a major focus. The Adaptive Battery feature will dole out background access to only the apps you use. A new auto brightness scheme has been devised. And the Android team has made changes to how background work runs on the CPU. All together, battery life should be batter (err, better) than ever.

To get a bit more detail about how all this works, we sat down with a pair of Android engineers: Benjamin Poiesz, Group Product Manager for the Android Framework, and Tim Murray, a Senior Staff Software Engineer for Android. And over the course of our second fireside Android chat, we learned a bit more about Android P overall and some specific things about how Google goes about diagnosing and tracking battery life across the range of the OS's install base.