In emails to The Verge, HTC and Motorola have clarified that they do not slow down phones as the batteries start wearing out. This comes in the wake of Apple's now controversial policy of slowing down phones with ageing batteries.
https://www.notebookcheck.net/HTC-and-Motorola-say-slowing-down-older-phones-is-not-their-cup-of-tea.275596.0.html