Do open apps actually drain battery?

[Stwutter]

Whenever I see a review of a new phone, the reviewer, quite naturally, scrolls through a dozen of more open apps on Lollipop to show lag, or the lack thereof.

I've almost always closed apps after using them, but I wondered if there is any real world battery drain from keeping these apps 'minimised', so to speak or if it makes no real difference? I've actually read that it can slightly improve battery life if the apps open are regularly used as it's not always being closed and then reopened...

Just curious...

Posted via the Android Central App

 

[Rukbat]

That depends. An app that's in RAM isn't necessarily an app that's running. An app that's running uses battery. How much depends on the app - some use almost none (my phone, running basically just Nova launcher and system apps in the background, used 25% battery in about 13 hours (with the screen off), some can drain the battery in a few hours (one that's constantly checking location, for instance). But a weak signal from the tower is even worse - the phone increases its transmitter power, and the transmitter running full power is a real battery hog.

The way Android normally works is that when you close an app (using the back button or Exit or Quit in the app's menu), the app stays in RAM, it's just not run. (Android decides when which app is run - that's how you can run more than 1 app at a time in a computer - each one gets a tiny time slice so it seems as if they're all running at the same time.) If Android's memory manager needs free RAM, it usually kills the least recently used app - marks the space that app is in as being free, so another app can be loaded there. (If the app is actually running, Android apps have to keep their own data any time it changes, so if they're killed, then brought back, they just pick up where they left off.) So unless you know exactly what's going on in the memory manager, you can't know when to run which app to keep it from being the least recently used one. With enough RAM, and few enough apps running, nothing may ever be killed. Multitasking the Android Way is a longer explanation by one of the programmers.

The best way to run Android is to let Android do its thing and not worry about it. The worst thing is to run a "RAM cleaner" or "Optimizer" app - they waste more battery and cause more lag than they fix. (I test ran Clean Droid for about a week - it's supposed to give better battery life. It killed my battery life. And that's one of the "good" ones.)

 

[zorak950]

It's also worth noting that what's in the recent apps switcher has nothing to do with what's running or in RAM. Just because it's there doesn't mean it's consuming any resources, and swiping it away doesn't close it if it is.