If you own an older iPhone and feel that your handset is getting slower, there could be a solution, get a new battery. It would appear that as the battery deteriorates on older iPhones, the CPU clock speed is reduced to preserve battery life.
This was recently confirmed by Reddit user TeckFire who has the battery replaced on his iPhone 6S. His handset had been getting slower and he decided to benchmark the handset. The benchmarks came out lower than they should be.
TeckFire had the battery on his iPhone 6S replaced and when he benchmarked the handset after the new battery he saw a considerable improvement in performance, have a look at the benchmarks below.
My iPhone 6S has been very slow these past few weeks, and even after updating multiple times, it was still slow. Couldn’t figure out why, but just thought that iOS 11 was still awful to me. Then I used my brother’s iPhone 6 Plus and his was… faster than mine? This is when I knew something was wrong. So, I did some research, and decided to replace my battery. Wear level was somewhere around 20% on my old battery. I did a Geekbench score, and found I was getting 1466 Single and 2512 Multi. This did not change wether 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 days charge.
So this could be a possible solution if your iPhone has been getting slower, it may be worth looking into replacing the battery on the handset.