Two weeks ago (November 16, 2018) I scheduled an appointment to replace my iPhone 6S battery at the Apple Store. I wanted to get this done while the price was still $29.99. A quick diagnostic and it was determined that I needed a new battery.
I left my phone with the technician and was asked to come back in an hour. My phone was ready right on time. Thanks Apple!
If you need your battery replaced under the “slowing down iPhones due to battery health”, you better hurry. It ends in 2018.
Drahusz 