Back in December my 5S decided to lock itself and the guys at O2 managed to reset it back to factory settings.
There has been an intermittent problem since iOS 8 came out that has affected my phone, and from wha I have read on the 'net loads of others, where no matter what the battery level is the phone powers down. I have had it do it anywhere between 21% and 65% of life left.
I logged into apple.com/uk/support/contact last week and before it had finished the online checks I got a notification that an iOS upgrade was ready.
I installed it and have had three days without it tripping out. Until today. Once again I logged in have now had to book a "genius" session at the Apple Store in Covent Garden for them to look at it as the "recommended" suggestion.
Let's see if they can fix it.