I got my iPhone 6S on release date. From then until now i've had a couple of times where the phone has just died from say 40%. It's been approx 40% battery one minute, i've gone to use it a little later & it tells me to charge it, so i do, the phone turns on & i'm back at 40%. Well i had my phone on me at work today & had been using it perfectly fine. The battery was somewhere between 60%-80%. I came to use it at the end of the working day & it's just a black screen. I try to power it on & it doesn't even tell me to charge it - black screen. I've had it plugged in to the mains for an hour now on 2 different cables - nothing, just a black screen. My phones are always in good order. Otterbox case, screen protectors, never dropped, not put in anything wet. Any idea on cause & solution?