Apple found to be throttling performance of iPhone's above 80% battery: https://www.reddit.com/r/apple/comments/7lkdur/i_went_to_the_apple_store_after_seeing_my/
I'd recommend everyone to run Geekbench and compare against expected results to see if your phones being throttled, regardless if your battery is healthy.
I'd recommend everyone to run Geekbench and compare against expected results to see if your phones being throttled, regardless if your battery is healthy.