I have a day 1 iPhone 6S, and it's still within warranty. It is running the most up to date version of iOS, and is always charged with OEM chargers. However, over the last week I have noticed that my phone will randomly shut off even though it wasn't <5 % battery left and when I try to turn it on the red battery indicator light comes on. This happened again today just now, and when I plugged the phone in it came back to life after 30 seconds with approximately 30% charge. Is this a known bug with the newest version of iOS or is this something I could take to Apple for a warranty fix?