I have an iPhone 6s, I got it when it was first released so I guess it's been about 1.5 years. I have had an issue happen 5-6 times. While using the phone it will die, just go blank as if the battery died. When I press the side button it shows the little plug telling you to plug it in. So I plug it in and finally the phone comes back on. But each time this happened I had 30% or more. It happened once with 60% charge. And as soon as I use the cord to get it to come back on, I can unplug the cord and use the phone for the rest of the day, so the batttery has plenty of power. What gives?