Sort of a long title, but this is particularly for people who upgrade from an iPhone 4 to an iPhone 5 and find their battery quickly draining and their iPhone 5 running hot. Everybody else, feel free to skip this message!
In a nutshell, I think restoring an iPhone 5 from your last iPhone 4 iCloud backup just brings in all sorts of junk the iPhone 5 can’t deal with and so things go awry.
My solution was to:
(1) Restore as a new iPhone after doing Settings > General > Reset > Erase All Content and Settings;
(2) Restore my apps, music, photo albums, etc., from iTunes.
After doing this, there are no more diagnostic error reports logged, the iPhone 5 runs cool (even though I’ve used it non-stop for the last couple of hours) and currently the battery is at 62% after 5 hours 40 minutes of usage. That’s quite good I think.
Nuisance-wise you have to tweak the stuff which gets synced from iTunes. For example, you have to rearrange your app icons and sign in to lots of places again. But it’s still much quicker than a restore from iCloud backup – which can take half a day!
So all-in-all my advice to people moving from an iPhone 4 to an iPhone 5 is to set it up as new iPhone, give it a new name (Settings > General > About > Name) and while connected to iTunes sync the stuff you want to sync to the new iPhone. Then you are ready to go except for sign-in and icon arrangement tweaks. In the end it’s faster and you don’t get the battery drain or the hot-running iPhone 5.