Hi, I have had this happen to me quite a lot recently. I will be on 30% battery, and then all of a sudden my phone just dies. Flat out. Refuses to turn on until I plug it in to a charger, where it will turn on and then claim it instantly has 26% battery or something like that. Any ideas how to fix this? This is happening on my iPhone 6 and also my gf's iPhone 6S.