iPhone 6 suddenly not charging

anyone else have this issue?

Starting one week ago my iPhone 6 had a drastic change in its ability to charge or hold a charge

It takes 8+ hours to fully charge and loses battery extremely fast. I went to the Genius Bar twice

first time they told me simple software glitch they fixed it rebooted and when I went home I saw no change, I went back last night and was basically told that I am used to my phone charging up very quickly (about 2 hrs) which is an over performance and that their diagnostic test which could not be completed.....meant that there was a software issue that may never be found be anyone so my options are to wipe the phone and start fresh which may or may not help or just buy the new one. Just looking to see if there is a better solution this makes no sense to me since nothing changed in the time the issue started.