This video was shot before Apple confirmed that battery wear impacts CPU performance.
Check story on the Verge here :
Battery Life App :
I have only been able to reproduce this on the 6S as I was able to borrow a device with a very worn battery. All other devices still perform at full CPU speed as they have limited battery wear. So luckily I could borrow a device for this video.
Fantastic Music by Ehrling:
Instagram : @Ehrlingofficial
Track : Champagne Ocean