iPhone 5S not turning on

Hi, I've had an iPhone 5S for better part of around 6 years now and obviously the battery has been pretty bad but I've got good use for it. Today it turned off (because the battery died)[this has happened plenty of times(turning off and i charge it and it turns on)] and I put it to charge but this time it wont turn on, it shows the battery pic to show its charging but its like the battery isnt strong enough to boot up. its been charging for almost 8 hours now pleas help. I tried the hard reset. its charging with the 5W adaptor in wall socket.