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This doesn't make any sense to me: why the iPhone doesn't automatically switch 3G off when connected to a wireless network?

I always thought iPhone did that since the very beginning and my battery lasted 4–6 hours on average per day. (I can almost swear that I remember Steve Jobs himself telling that in the stage back then)

Then a friend of mine asked me why I don't switch off the 3G when I am in the office to save some battery instead of charging it at my desk so in case I had to get out it was fully charged back again.

So, I tried... Boy, it was a huge difference! My iPhone's battery will last 10–13 hours on average. That means usually I can get back home from work and have my phone still working in my pocket.

Any ideas?

EDIT: my question is about worse battery performance when 3G is enabled. (Even though not supposed to be used) And I believe this isn't related to me, but to any iPhone user really.

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    So you're asking if they 3G actually switches off? Why it does not happen to you? Or about the battery improvement you experienced? – Thecafremo Jan 9 '14 at 20:23
  • When I am on wifi, my iPhone always uses that instead of the cellular data network and my battery life is great. The iPhone is very much wifi-based and will attempt to connect, and use it every time it can. I never turn off cellular data on a regular basis. – bassplayer7 Jan 9 '14 at 21:17
  • Are you asking why Apple doesn't provide such a feature as part of iOS? – nohillside♦ Jan 10 '14 at 5:37
  • @Thecafremo my question is about worse battery performance when 3G is enabled. (eventhough not supposed to be used) And I believe this isn't related to me, but to any iPhone user really. Thank you. – Ali Jan 10 '14 at 6:34
  • @bassplayer7 precisely! But why not, since it's a huge battery improvement? I mean toggling that setting on and off manually doesn't make any sense and I'm sure they could do that automatically in the background. So although wifi is being used, 3G will still suck up the battery. – Ali Jan 10 '14 at 6:37
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Although your iPhone will use WiFi when available, that's only to save your cellular data limit being reached as quickly. Your iPhone keeps the 3G antennas active (while the internet is in use) for the following reasons;

  • In case you have 'flaky' WiFi; your iPhone will switch between WiFi and cellular without you noticing to keep a reliable connection working source*
  • In case you leave WiFi range; your iPhone can then immediately switch to cellular and use it right away without any delays.
  • In case your WiFi network doesn't have a 'proper' internet connection; if your WiFi network can't load certain pages (either because it's configured incorrectly, or because of a fault/security settings) your iPhone will use cellular to load those pages if possible. **

So, to answer your question, the iPhone keeps your 3G connection live while the phone is using the internet in some way so you can have a reliable connection. Your phone will only turn it off automatically when/if the phone is trying to save power.

*I believe the toggle to enable/disable this feature has been removed, but the feature still exists (and remains always on).

**I've seen this happen with those WiFi networks which would make you fill in a form/login before using the connection. The phone would be connected to WiFi, but apps would be using 3G to load new content as I was not yet logged in

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  • Thanks for a nice explanation. Could you please point out an "official" reference (if there is one) where you get this information please? – Ali Jan 10 '14 at 11:06
  • I've edited my answer to include sources – Joseph Jan 10 '14 at 13:29
  • Quote: "I've seen this happen with those WiFi networks which would make you fill in a form/login before using the connection. The phone would be connected to WiFi, but apps would be using 3G to load new content as I was not yet logged in". I don't think this is correct, since in that case Wi–Fi network would allow you to navigate (i.e., by redirect) to a predefined page, but block everywhere else, unless you’re logged in. – Ali Apr 30 '14 at 14:19
  • The Wifi blocks access to most pages when not logged in, so the iPhone automatically uses 3G to get access to them. – Joseph May 1 '14 at 11:23
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Such a feature was never a part of iOS. If you want to request it from Apple, use the contact details on the Apple website.

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  • Don't you think that should be though? Anyway, I will go ahead and accept your answer. Thank you! – Ali Jan 10 '14 at 11:04
  • Discussions about potential iOS features are off-topic on AskDifferent – nohillside♦ Jan 10 '14 at 13:24
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The iPhone will switch from 3g to a known wifi network, that is, one that it has connected to before. At your office go to settings > wifi and connect to your wifi network. From then on it should automatically connect when you are in range. If the phone doesn't remember the network, connect to iTunes, backup and restore.

Also, if you have a weak or intermittent 3g signal the phone will use a lot of power searching for and trying to connect to the network. I have this problem every time I visit my friends in the mountains. If you have a good wifi and 3g signal then your problem may be hardware or software related. If you're near an Apple store they can test the hardware for you.

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  • See my edit to the original question please. Thank you! – Ali Jan 10 '14 at 6:41
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Most of people are using 3 or 4 g with public connection (wifi) on.This will never work .This might create issues , a slow connection , beside this, when they can not be switched manually , the battery is twice weaker or more.

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  • I am not sure how this is an answer. Can you clarify as I can't understand what you are getting at? – Allan Jul 13 '16 at 16:49
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As of iOS 9 there’s an option to disable “Wi-Fi Assist” that will effectively disable cellular data usage when connected to a Wi-Fi (or rather when disabled won’t automatically use cellular data to assist poor Wi-Fi connectivity.)

Follow: Settings.app > Cellular > (at the very bottom) Wi-Fi Assist toggle:

enter image description here

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