I was talking to someone at work who has an iPhone 5, I've just got a secondhand one myself too. He was saying his 5 turns off at 20-30% since updating to iOS 7 (so far mine doesn't, ran it down to 19% with no issues). He said on forums, not sure which ones though that there is a bug of sorts with the battery algorithm that affects the 5 which makes it think the battery's prematurely flat at these levels and shuts the phone off. Apparently it's because it's optimised for the iPad and it's larger capacity battery. I've searched the forums here for this and found no mention of this, mainly hardware issues or debates on if it is software or not. Is there any truth in this, or is it a myth? If it is software, is it something that will be fixed in the upcoming iOS 7.1 update?