Where can I get instructions for battery replacement for a HTC One M8?
Did you try a web search? When I did, I was reminded the battery isn't user replaceable and requires physically removing the back of the phone off in order to access the battery.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.
We depend a lot on our phones nowadays that it is critical for them to work correctly at all times. To be on the same page and provide the correct resolution, tell us more. What is the reason you want to replace the battery for the HTC One M8? How's everything with your Verizon service? Keep in mind that the M8 comes with a non-removable battery. https://www.verizonwireless.com/support/knowledge-base-115358/