my iphone 6 won't start

my iphone 6, over the past give or take month has been having battery issues, reluctant to bring it to be fixed i just lived with it. now, the phone has basically turned off, when i attempt to hold down the power button, the booting apple logo shows up, but goes away after about three seconds, the screen is black but still lit, this goes on for like five minutes, then turns off. i have tried everything, plugging it in, waiting for the power to run out then plugging it in, i tried to restore it from my computer but that didn't work.