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When your iPhone battery is "almost" dead, it turn off, and then if you want to turn it on again it loads this very informative graphic:

Battery is low picture

The problem is that when you turn on "power button" this picture show up almost immediately, without starting up operating system or anything.

I just wonder how they done it ? Is this behaviour is hardcoded in hardware ? Is it configurable and could be changed (to flatter design) when iOS 7 will come ?

My understanding is that, they have to make it in hardware, make special circuit that when battery sensor inform about very low battery status, show this picture.

PS: I saw similar behaviour in Nexus 7 (2013)

  • @patrix Why answers to this question be opinions ? If somebody don't know just do not answer this question. That's it, I see no reason to put this question "on hold". – Paul Brewczynski Sep 15 '13 at 12:59
  • I'm going to reopen this but a thread on Ask Different Meta might be needed to sort out whether to keep this open or not. Clearly, you're asking about how the hardware / firmware / software interact, but there's doesn't seem to be a tie to anything practical which would be my main complaint about this question. Perhaps some editing or clarification will help the question out and also get you an answer you can use. – bmike Sep 15 '13 at 13:29
  • it is hardcoded in the pram, it is not programmable. – Ruskes Sep 15 '13 at 19:27
  • 1
    If the question needs to be reworded to be practical, might I suggest "How can I modify my iPhone to display a grumpycat picture when the battery is low"? – gabedwrds Sep 16 '13 at 2:38
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I believe it's just an early stage of the bootloader that checks to see if the battery has enough charge before going on to boot iOS. It's no different from being able to display the Apple logo while iOS is booting.

If you download one of the IPSW files (iOS images), you can unzip it and find several images inside - applelogo, batterylow, glyphplugin, and so on. A full listing can be found on this page: IPSW File Format, and I also came across this page which has instructions for replacing the low battery image with something else (essentially just replacing the file inside the IPSW with another one in the correct format).

That would seem to indicate that iOS 7 will (or does) have a new version of the image for all devices, just like it has a flatter Apple logo at boot time.

  • I can confirm that the update to iOS 7 changed these images on my iPhone 4. As long as you want to use the ones Apple delivered, no jailbreaking is required. – bmike Sep 18 '13 at 19:12

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