iOS 4 - Battery Vampire?

[Michael Knutson]

<div class='os_post_top_link'><a href='http://www.pcworld.com/businesscenter/article/199974/the_iphone_ios4s_battery_bummer_the_power_vampire.html?tk=hp_new' target='_blank'>http://www.pcworld.com/businesscent....html?tk=hp_new</a><br /><br /></div><p><em>"I upgraded my factory-unlocked iPhone 3GS to iOS 4 just prior to leaving on a six-day trip to British Columbia. My service provider in the US is T-Mobile, and I expected to use Rogers without a problem in Canada. Well, I was in for a rude surprise ..."</em></p><p><img src="http://images.thoughtsmedia.com/resizer/thumbs/size/600/at/auto/1277143092.usr17748.jpg" style="border: 1px solid #d2d2bb;" /></p><p>Having no data plan with Rogers while in Vancouver, I was prepared to use wi-fi whenever possible, with the expectation that it (wi-fi) would impact battery life no more than it did on v3.1.3. Was I wrong! Using about ten minutes of wi-fi dropped the battery to about 90%, and that was just emailing. Another five minutes of light browsing dropped it another five percent. Something just felt different (wrong) about iOS 4.<MORE /></p><p>I began tinkering with the OS, and decided that I'd see just what was running in the background, or more accurately suspended, did the magic keystrokes to get inside, and discovered several dozen things sitting there idle. Killing them one after another, I got everything stopped, and then went back to my home screen. Now it was down to 80% battery remaining. &nbsp;So something was definitely draining the battery.</p><p>Back home, and time for some research. PC World reports that users are complaining (<a href="http://www.pcworld.com/businesscenter/article/199974/the_iphone_ios4s_battery_bummer_the_power_vampire.html?tk=hp_new" target="_blank">link</a>) that battery life is now half, or less of what it was prior to the upgrade. One user reported losing 1% of battery life every 2 minutes with only iOS 4 running. So I wasn't just imagining this. It has been reported to Apple, and their tech Support forums now have another issue to hash around. As a long-time IT guy, I should know that a DOT ZERO version can buggy. Now we wait for the first set of fixes.</p>

[Jason Dunn]

I've been running iOS4 on my 2G iPod Touch since it first came out, and haven't noticed anything out of the ordinary so far - but I can't multi-task with the 2G iPod Touch. Multi-tasking seems to be the common thread in the complaints...if that's what it ends up being, that will be rather ironic, because Apple always insisted the reason there was no multi-tasking - right up until THEY did it of course - was that the multi-tasking that everyone else did was hard on the battery. :rolleyes:

[Jeff Campbell]

Multi-tasking seems to be the common thread in the complaints..

I was running into battery problem with my iPhone 4, while it was lasting longer than my 3GS, it still wasn't close to what some of the reports for battery life were...so when I double clicked the home button I saw how many apps were still open! I closed all the apps and my battery life improved dramatically.... rather annoying!

[rockinthesixstring]

Would you mind describing what the "Magic Keystrokes" are? I'd love to know how to view the running tasks.

[Sven Johannsen]

And a budding market for iPhone task managers appears. Maybe Apple should allow apps to include an X that closes them ;)

[Jeff Campbell]

Would you mind describing what the "Magic Keystrokes" are? I'd love to know how to view the running tasks.

Yep, pretty easy...just double click on the home button and it opens up a window at the bottom of the screen, you can see all the apps that are still running listed there. To close them, touch and hold your finger on one of the icons (like you would if you were going to move apps around on your screen) and in a second or two you get into "edit" mode, and a minus sign appears on upper corner of the app icon. Touch the minus sign and the app closes.

[rockinthesixstring]

Ah, I was thinking of some hidden function. I have a 3G that cannot multitask... but there are still some battery issues with iOS4

[Michael Knutson]

I've tried restoring a fresh copy of iOS 4 on my 3GS, and that seems to have made it a tiny bit better, but still not like I was expecting. I too was astounded at the number of things sitting dormant in the background, so I've started training myself to "kill" everything running before finishing up for the day. I agree that there is a potential market for 'task manager' for iPhone, if Apple allows it ...

My 3G test phone has been downgraded back to 3.1.3, and the battery life seems back to normal.

Yes, this is indeed a DOT ZERO version of iOS 4!

I wonder how Android addresses this issue of battery drain with multi-tasking, or fast task switching.

[Michael Knutson]

Yep, pretty easy...just double click on the home button and it opens up a window at the bottom of the screen, you can see all the apps that are still running listed there. To close them, touch and hold your finger on one of the icons (like you would if you were going to move apps around on your screen) and in a second or two you get into "edit" mode, and a minus sign appears on upper corner of the app icon. Touch the minus sign and the app closes.

I've read it described as "icon shimmy." pretty funny ...

[Jerry Raia]

I too have noticed increased battery drain on my 3GS with iOS4. I haven't been too religious about closing the running apps though.

[Dyvim]

Note that the list you see at the bottom isn't necessarily a list of running apps. It's more like a list of most recently launched apps. If they haven't been recompiled with the iOS4 SDK they're not really running at all- e.g. Skype, Facebook, The Weather Channel, etc. Removing it from the list does kill the app if it is running. But some of the apps in the list (esp. those further to the right) will have already been killed by the OS when memory was low so they're not really running anyway (you'll know because those apps will launch from scratch and not instantly be available where you left off). This is more apparent on the 3GS than on the 4, most likely due to the lower memory (256MB vs. 512MB).

The way that the OS suspends the apps (terminates those that haven't been updated for iOS4) doesn't seem like there'd be much cause for battery drain, so I'm not convinced. I vote for differences in Exchange ActiveSync implementation and Push notifications rather than multi-tasking as the cause of extra battery drain.

Anyway, here's hoping that 4.0.1 brings improved battery life.

[Bob12]

FWIW: On my iP4, leaving the programs idling doesn't seem to have much of an impact on my battery life; or, if it does, without the background idling, it'd be downright incredible. After 33 hours of normal use (frequent checks of e-mail, several phone calls, numerous weather/web searches, etc.) the battery was at 33%. I did not have wi-fi on during that time and bluetooth was on for about two hours.

[Jason Dunn]

I've tried restoring a fresh copy of iOS 4 on my 3GS, and that seems to have made it a tiny bit better, but still not like I was expecting. I too was astounded at the number of things sitting dormant in the background, so I've started training myself to "kill" everything running before finishing up for the day.

Here's what I don't quite grasp, and maybe it's because I don't have a new enough iPod Touch to see the multi-tasking...99% of the time, I wouldn't want to have the app I'm using running in the background. I'm perfectly fine having it re-launch and restore the previous state because it does that quite well.

I had assumed, obviously erroneously, that only certain applications coded a certain way by developers would multi-task...apps that really needed to stay open in the background (streaming audio, GPS, etc.). But the way people here are describing it, it sounds like every app they use keeps running...which makes no sense to me. :confused:

[Dyvim]

I had assumed, obviously erroneously, that only certain applications coded a certain way by developers would multi-task...apps that really needed to stay open in the background (streaming audio, GPS, etc.). But the way people here are describing it, it sounds like every app they use keeps running...which makes no sense to me. :confused:
The way I understand it (as a developer), there are 3 kinds of apps:
1. older apps not recompiled with iOS4 SDK- these are terminated when you launch another app just like on all previous versions of the OS. (You'll still see them in that multi-tasking launcher but that doesn't mean anything.)
2. newer apps recompiled with iOS4 SDK that don't need to multitask. These get suspended. They still use memory but shouldn't occupy any CPU cycles- i.e. should cause no battery drain. So basically they gain fast app switching.
3. newer apps recompiled with iOS4 SDK that do need to multitask (e.g. audio, GPS, VOIP). These get partially suspended but get specific callbacks from the OS to perform their tasks. So they're running, but they're using less CPU (read battery) than they would if they were in the foreground since they're not refreshing their displays or monitoring user input. There are very strict rules these apps have to follow (like severing network connections, stopping use of things like OpenGL, releasing shared resources like Calendar and Address Book) that if they don't follow will result in their being terminated.

If you haven't updated a given app since the iOS4 launch, then it's type #1 and it's not multi-tasking anyway (and some apps updated since then like Amazon's Kindle still don't seem to multi-task).

Any time the system needs memory, it will send memory low warnings to running apps. If they're well written, they'll free cached resources, etc. If the system still needs memory it will start terminating background apps.

That "multitasking bar" of recently launched apps you see when you double-click Home is a lot like the tabs in Mobile Safari: when you switch between them, they may in fact be cached and load quickly (app was suspended) or they may need to be reloaded from scratch (app was terminated and had to relaunch). Multitasking on iPhone 3GS seems a lot like Safari tabs in iPhone 3G and earlier: maybe 2-4 get cached but beyond that things start getting terminated. iPhone 4 seems to allow quite a few to coexist before it starts freeing up memory by killing older apps.

[Jeff Campbell]

I vote for differences in Exchange ActiveSync implementation and Push notifications rather than multi-tasking as the cause of extra battery drain.

Anyway, here's hoping that 4.0.1 brings improved battery life.

I think you are right, because after I drained my iPhone 4 and charged it back up, I decided to test and see if the apps were the problem or my battery just needed a slap...I've had multiple apps in that tray all day and after 9 hours, with some email texting and one phone call thrown in, and bluetooth left on all day, I'm down to about 84% so much much battery life