Battery was shot
Somewhat lengthier than I thought. I am a returning customer of ifixit. Replaced my old Iphone 5 battery when the same thing happened to it. That fix was much easier than the 6. I don't know where the !&&* Apple buys their adhesive for the battery backing, but holy !&&* it took me a while to get it off. Hair dryer and all, I almost broke my credit card trying to get the battery off.
Patience and incessant shoving of the card into the adhesive seemed to take it off. After a smooth rest of the installation, I powered up my phone to realize that it coudn't seem to find service. I restarted the phone, but it remained "searching" for signal. Thinking I maybe damaged the sim card module in the phone, I removed the sim card and it put it back in. Thankfully it worked.
Replacement battery from Ifixit is solid - its only gone down 9 percent in the last 4 hours. Very happy with my second purchase and fix from ifixit. Thanks
Don't freak out when you lose a iphone 6 screw. They sent me replacements in the kit :)