[cjbprime]

My 6P's battery is trash after a year and not replaceable :(

[ToastyMallows]

If you're brave it looks like you can replace it in only 5 steps. The caveat being that those 5 steps look very difficult, and in some cases require special tools.

https://www.ifixit.com/Teardown/Nexus+6P+Teardown/51660