A reddit thread has popped up in which redditor TeckFire alleges that his iPhone 6 Plus had been slug-like in performance since upgrading to iOS 11. Anecdotally, iPhone users tend to complain every year when a new iOS release becomes public, alleging that Apple is purposely slowing down older devices. However, TeckFire has found that there might actually be some truth to those claims.
TeckFire performed some Geekbench tests on his iPhone 6 Plus with its original battery, then performed the same tests after replacing it with a brand-new battery:
I did a Geekbench score, and found I was getting 1466 Single and 2512 Multi. This did not change whether I had low power mode on or off. After changing my battery, I did another test to check if it was just a placebo. Nope. 2526 Single and 4456 Multi. From what I can tell, Apple slows down phones when their battery gets too low, so you can still have a full day’s charge.
Other users in the reddit thread have chimed in, and the overarching theory appears to be that Apple implemented changes in iOS 10.2.1 and later that were meant to help prevent premature iPhone shutdowns. Some iPhone 6s users were experiencing problems where their batteries would dramatically drop from the 20 to 30 percent range down to zero in just a few minutes (or seconds), prompting the device to shut down – iOS 10.2.1 was released to address this problem.
Redditors are speculating that Apple was (and still is) throttling CPU performance to help preserve battery life (and hence prevent shutdowns), which would explain TeckFire's findings and reports that iPhone users were seeing reduced performance after a major iOS update.
At this point, there is no word from Apple on these new revelations, and it's doubtful that we will receive one. However, the reddit thread, which has over 600 comments at this point, is an interesting read.