I upgraded a failing battery about 7months ago. iPhone 6 was fine.
WHY then after upgrading to iOS 11, phone becomes sluggish, typing on the keyboard sometimes doesn’t give feedback for SEVERAL SECONDS until it spits out a burst of text in one shot (sometimes even missing CAPS changes), switching apps is a long ordeal. Don’t get me started on Apple Car (became an unusable slow crap), Siri while driving sometimes takes A MINUTE to process a simple command such as “call John using FaceTime audio”, etc...
Alright MR, I’m planning to use the battery replacement program, sure why not, let’s give it a try, maybe the batteries are so massively crap that they snap not at one year use but at 6months.
I still have the feeling that, after the upgrade, issues with sluggishness, keyboard, AppleCar features, etc won’t magically disappear.