Sold my M9 last week for the lack of replaceable battery. I was not the original owner. No "warranty".
The phone was great, but it is 2 yrs from release and I didn't want to get stuck with a brick sometime in the 3rd yr.
ifix says it is a difficult task to replace the battery. I expect The phone may never be the same, like a wrecked car after repair. With a lack of users reporting results of a repair, I had to jump off.
Got a barely used Note 4, after my wife and friend replaced their batteries and said they would buy the phone again.