> Adaptive Battery, in a nutshell, is about figuring out which apps you use frequently and keeping those apps in memory, while the apps you don’t use often are purged once you’re finished with them. Put another way, Android Pie can adapt to your usage patterns so that it only spends battery power on the apps Adaptive Battery thinks you’ll need. https://venturebeat.com/2018/08/28/how-android-pies-adaptive...

I don't know. Wouldn't be easier to simply close the app when a user closes it ?

Fully-closing apps requires them to re-initialize them from scratch after each re-open, which is cpu-heavy (thus also battery-heavy) and slow.

A frequent usage pattern, also, is quickly switching between several apps. There's no definite “close” on mobiles apart from force-quits, which are unhappy for all apps, too.

> Fully-closing apps requires them to re-initialize them from scratch after each re-open, which is cpu-heavy (thus also battery-heavy) and slow.

Thanks for the explanation, I didn't know starting from scratch was so expensive. I had always wondered (and fumed) about that but it makes more sense now.

Android is designed so that users never "close" an app (there's no close button); instead, they switch between apps. The system closes apps in the background when necessary to free memory, but all apps are supposed to save and restore their state so that the user is presented with the illusion that the app never stopped running.

This is untrue. You can close an app manually by pressing the bottom right software button, which shows your foreground apps, and then swiping the app window off the screen.

The state is lost and, for most apps, background processes are killed.