[One (M8) Q&A, Help & Troubleshooting] Casetheace:
I recently had to replace my battery in the m8. I managed to find a retailor online, ordered it, came with a install tool and double sided tape to replace the one used before for the speaker covers on top and bottom.

There is so little into on this online, I followed a YouTube video on replacing the digitizer of the phone to learn how to open the phone to replace the battery. I can say from experience its pretty easy, more intimating then anything after watching the video first. After applying heat to phone, I used a hair dryer. Of cource removing the screws that are found after removing the speaker covers that are removed after placing heat. The video I saw suggested guitar pics. I had none and have no idea where to find them. So I used some old credit cards, along with gift cards. The phone was pretty easy to remove from shell after heat. Where I screwed up, and its not mentioned in any videos I saw. THERE IS A SMALL RIBBON THAT SPLICES FROM ANOTHER LARGER RIBBON NEAR OR EXACT LOCATION OF AUDIO BUTTONS ON SIDE OF PHONE. I believe that when opening the phone from frame I may have ripped this ribbon by opening it with a credit card and ever so silently pushing the card upwards to remove the phone from the frame. After replacing the battery and replacing the phone in frame, on first boot my audio buttons don't work. I removed the phone from frame and that's when I noticed the small ribbon that wraps around the side of the phone easily ripple able when using anything along the side of the phone to remove the frame. It's not mentioned in any videos I watched on YouTube, so BEWARE. I'm hoping if anyone knows if this ribbon is replace able and maybe how it might be replaced?? Also if anyone can confirm this ribbon is used for audio connection to buttons?? After noticing the F.UP, I can see how each connector is used to hit the audio up and down but am still puzzled as to why it needs this ribbon I believe. Would think that the audio connection after receiving a hit on up or down would send whatever signal thru the phone onto a much larger ribbon to the motherboard which is on top of the battery. Yes its the same as a small ribbon connection, but I don't see the reason of needing this separate ribbon that appears is just for audio, spliced from a larger ribbon. So I'm hoping that someone can confirm that this is the intenal setup and yes this ribbon is for audio. So that I can maybe replace it, or at least stop me from trying to figure out other reasons of why. But I at least wanted to warn other people of this before they tried to replace the battery themselves. Also if you do replace it and after booting phone on either side it appears that you damaged the digitizer cause maybe one or two buttons don't work on keyboard. Its most likely cause the screws on the frame under speaker covers are to tight. I did that also and thought I broke the digitizer removing the battery. But after removing screw's and enter the booting up the phone with no screw's but in frame, all keyboard functions worked. I then screwed each screw in and applied pressure , then turned phone on to make sure it wasn't to much. Just don't tighting screws with phone booted on, believe you could get a static charge and screw up phone. Hope this guide and question helps anyone replacing battery. Mine failed after using custom ROMs on 5.1.1 , phone began to not stayed charged for more then a hour, also wouldn't even accept a charge. Tried all other fixes, calibrating battery and all. After replacing phone works fine accept for audio which is a pain in the A$$ cause can't manually boot to bootloader on boot by hand.