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Public Service Announcement: You Should Not Force Quit Apps on iOS (daringfireball.net)
John Gruber, writing for DaringFireball: The single biggest misconception about iOS is that it's good digital hygiene to force quit apps that you aren't using. The idea is that apps in the background are locking up unnecessary RAM and consuming unnecessary CPU cycles, thus hurting performance and wasting battery life. That's not how iOS works. The iOS system is designed so that none of the above justifications for force quitting are true. Apps in the background are effectively "frozen", severely limiting what they can do in the background and freeing up the RAM they were using. iOS is really, really good at this. It is so good at this that unfreezing a frozen app takes up way less CPU (and energy) than relaunching an app that had been force quit. Not only does force quitting your apps not help, it actually hurts. Your battery life will be worse and it will take much longer to switch apps if you force quit apps in the background. [...] In fact, apps frozen in the background on iOS unfreeze so quickly that I think it actually helps perpetuate the myth that you should force quit them: if you're worried that background apps are draining your battery and you see how quickly they load from the background, it's a reasonable assumption to believe that they never stopped running. But they do. They really do get frozen, the RAM they were using really does get reclaimed by the system, and they really do unfreeze and come back to life that quickly.
I have an iphone 6s, and I see the location icon come on when I check the weather (using the native app), because it is set to reporting local weather. Mostly, it goes away in a bit - but I have seen the icon stay on many times even when I have moved away from the weather app. I have to manually kill the weather app to make the location tracking go away.
5 or so years ago, it was definitely clear that leaving apps open was causing battery drain, and I obsessively closed everything as soon as I was done.
About a year ago I heard someone from Apple suggest it wasn't necessary any longer, and for the most part I leave things up and it seems to be true that they're not tremendous battery hogs.
Except Google Maps, of course. That burns through something like 1% of my battery every minute, and definitely keeps working even in the background. I will look stuff up, kill it, and repeat as necessary many times over rather than leaving it open any longer than I need to.
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In my experience, iOS' "Low Power Mode" works extremely well in terms of extending a phone's remaining battery life. Of course, one of the things it does is stop the background execution of most apps.
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Force quit is there because sometimes you need to do it.
The OS is good, but it's not magic. It can't always tell if an app somebody else coded is in an inconsistent or errored state.
There's a lot of uninformed computer voodoo that users buy in to. One of them is that force quiting background apps is a good idea. If there's any real benefit it's in their head.
iOS is /really/ good at suspending apps. I've had apps keep their state /between iOS upgrades/ - Exited a game, and came back to it weeks later after a major iOS release. Picked up exactly where it left off.
settings->battery. Scroll to bottom for a report of how much battery each app has used. View it as last 24 hours, or as last 7 days. and FYI, (for me) Apple Mail, when connected to a corporate exchange server, sucks battery in the background. 30% overnight iphone 6s IOS 10.3
You would be imagining incorrectly then.
iOS has not had to "fake" multi-tasking for quite a few versions now. Why base your imaginings on that?
iOS now selectively freezes applications on a per-thread basis, depending on the services identified as being handled by each thread, and orders the app to save state preparatory to being potentially killed shortly after is has been backgrounded in the UI. This effectively makes most apps flash-frozen in RAM, and all apps instantly killable on-demand if memory pressure demands it.
Going into the app switcher and "killing" them just wastes your time, and your device's battery, sending deallocation commands to things that are only there because the RAM hasn't been requested for anything else yet, or even worse, just loading the saved thumbnail images of the last seen state of an app that has ALREADY been deallocated (eating up some of your RAM as it does so) so you can flick your thumb upward on them and remove them from the list. There is honestly no point to this exercise except to indulge your OCD.
The real savings is in the designated threads for designated services: They are policed. A thread that is allowed to continue running in order to keep playing you music, for example, is actually disallowed from claiming more than a certain percentage of CPU time, and disallowed from accessing certain frameworks.
That said, some applications try to abuse this. A few versions and iOS updates back, there was a furor over the way Facebook behaved when it was backgrounded. It actually spun up a fake "music" thread, playing dead silence, and used it to fetch more network data than it was otherwise allowed, which in turn drained battery faster.
If you suspect there are apps doing nefarious crap like this, go to settings > general > usage > battery and look at the statistics. The culprit in your declining battery will be shown right there. If you want you can hit a few switches and deny that app all background activity.