I know apparently it’s not a good idea to close apps on your iPhone to save on battery. I’ve read questions and answers like Does force closing apps have any benefit on iOS devices? but it still doesn’t quite gel with me. Sometimes I have found over 50 apps running, so not closing them makes no sense.
Maybe I’m a bit of an old chook and you just can’t teach old dogs new tricks, but can someone here explain WHY it’s better to just keep all these apps running? And when I say “explain” I mean in layman’s terms so I can understand.
Best Answer
You’re not alone. People are just used to their desktop computer habits, and it’s understandable they carry these habits over to their iPhones and iPads.
However, let me try and explain this using an analogy:
Imagine it’s a hot day and you’re outside gardening. You get thirsty, so you go inside to the kitchen, grab a large glass, put some ice in it, and fill it with water. You then drink half of it and empty the rest in the sink before going back outside. Not long later, you get thirsty again, so you go back inside to the kitchen, grab the same glass, put some ice in it, and fill it with water. Again you only drink half of it and empty the rest in the sink!
The above workflow just doesn’t really make sense. Why wouldn’t you take the glass outside with you? And, you’re not only wasting water by emptying it, but you’re spending more time and energy getting that water again.
Likewise, when you quit an app you’re actually using some battery power in the process of doing so (e.g. clearing it from RAM, etc) and then again later when you have to launch it again and load it back into RAM.
So, for a great majority of the time it’s best to leave apps open. Even though they’re open, they’re really just sitting in a type of suspended mode that isn’t using any battery power whatsoever. Yes, the app is still loaded in RAM and taking space, but it’s not actually doing anything - it’s just lying there dormant. And, because it’s not using any battery power in this state, there’s no advantage to quitting it from a battery conservation point of view - especially if it’s an app you know you’re going to be using again and again throughout the day.
There’s also really no advantage to force quitting an app because iOS itself will do this for you if/when it needs to in order to free up RAM. So if you have 50 apps open and they stay open, then iOS hasn’t been pushed to the extent of needing to close any of them to free up memory.
Now, like anything, there are always exceptions to the rule (such as apps that have to perform background tasks). An example of this is one that plays music while you’re doing other things with your phone, or one that’s downloading content in the background, or one that’s counting how many steps you walk in a day, etc. However, iOS has an extremely efficient process for managing background apps/tasks and if you choose to quit these you’re basically saying you don’t trust the operating system to do its job properly.
So, feel free to quit your apps when you have to (e.g. because it’s frozen, etc), but don’t do it to conserve battery power. In fact, if you do, you’ll be achieving the opposite and using more battery power throughout the day!
Summary
Most apps in the App Switcher will be in a suspended state - this means they're not: visible on screen, executing code, using the CPU or GPU, or using the battery. However, they are still resident in memory until they are purged (if necessary) by the system to free up memory:
Source: See Table 2-3 within the first reference link at end of this answer.
The only apps actually running on your iPhone at any given point in time are the active app (i.e. the one visible on screen) and any others working in the background. (Note: There are some temporary exceptions to this in the case of apps that still need time to complete executing code they already started while they were active - typically this is only in the order of seconds but could theoretically extend to over a minute.).
References