TL;DR I have an early 2015 Macbook Pro (stock features), running Yosemite (not sure of the version). I've tried SMC and PRAM resets, taking the battery out, and external mouse and keyboard with limited success.
A few months ago, the internal keyboard and trackpad would work intermittently, but after a week or so, they quit working altogether. The power button still works. Though, I'm now experiencing issues with the computer's bootup. Sometimes when I boot it up, it shows the Apple logo and then quits. This didn't happen before. And before I get into it, the internal keyboard and trackpad don't work during bootup either. I can't use them to boot into safe mode or reset the PRAM or SMC. I need an external keyboard for that.
I was traveling in Southeast Asia at the time with no Apple store within a few thousand miles, so I didn't go see anyone about it. I read forum after forum, and asked questions. I was told (and convinced) by several people that the problem was a swollen battery. In Malaysia, I took the bottom off of my computer, which seemed to make it a little more stable. It created more room in the computer body, and lent credibility to the swollen battery idea. In Asia, I just couldn't get what I needed to take the battery out and try it. I went to an internet cafe in Indonesia and borrowed a mouse and keyboard. I was hoping to install a driver to use my iPhone as a new wireless mouse and keyboard. My experience was less than stellar. The computer was super jumpy. The mouse and keyboard barely worked. I'm not sure if it was the computer's fault or the cheap equipment at the cafe. Restarting the computer didn't seem to do anything.
Fast forward to London, I was at my mother-in-law's house. She had the security I needed to work on my computer as well as an external mouse and keyboard. They worked great! The computer was not jumpy like it was in Indonesia. I took the battery out (please don't give me flack about how my battery is non-removable, I know what I'm doing). To my surprise, the internal keyboard and trackpad still didn't work.
I'm back in Berlin where I now could go to an Apple store, but I'm also in the best place to work on it myself, and I'd like to take one last stab at it before I pay some extortionate fee to have it fixed. Does anyone have any ideas, that don't have to do with the battery, of why this could happen to a pretty new computer?