Right now, your phone is still one of the best in the world, but you're likely to start to seeing battery life problems and everything slow down over the next year. (howtogeek.com)
Many iPhone and iPad users have complained about battery life problems since upgrading to iOS 11. (technowize.com)
How do you fix battery life problems after updating to iOS 11.3 or upgrading to iPhone 8 or iPhone X? (imore.com)