When I first heard about this, it was apparently due to Apple throttling the CPU when the battery started getting old and losing capacity. When the battery gets

When I first heard about this, it was apparently due to Apple throttling the CPU when the battery started getting old and losing capacity. When the battery gets older, it keeps less charge and therefore, if you want the battery to last a reasonable amount of time, you'd need to lower the power usage. I recently got my iPhone 6S battery upgraded since it started shutting off randomly below 40%, especially in the cold. I got my battery changed for free due to the Apple 6S battery exchange program. Today the phone feels just as fast as I want it to. I have zero incentive to upgrade, and I'm even on iOS 11 which I've had zero problems with. I know of other people whose phones got faster after switching out the battery. In my opinion, after 2 years or so, you just need to change the battery. I wish Apple made it easier to see the health of the battery, and maybe a button that would send you a package with a return sticker so you could mail your phone in and get the battery changed in a day or two.