iphone 4s keeps cutting off

I got my 4s last Christmas and about two days ago, my phone cut off at 13% and wouldn't cut back on until tonight around 11p.m. I had it on the charger for about four hours the first day it shut off and wouldn't turn back on and that did nothing. Now its back off and its only been two hours, I've tried it in different chargers but the symbol that usually pops up telling you to plug your device in, doesn't even show anymore. Help please