Chosen Solution
So, I replaced the screen of my iPhone 6. I had not used it for two months after cracking the screen. Now that I fixed it, the phone has yet to fully boot up. It does show the apple logo and then the low battery. But, this has been repeating since I started to charge it an hour ago. Should I leave it be and let it charge or is there another option?
Just leave it charge, for an hour or so. If it doesn’t get any better you may have to replace the battery. Which is an easy fix. Keep us posted.