My battery on my s4 is epic. A day of heavy use on the internet, videos texts whatsapp etc and it still has over 20% left. 7 am till mid night roughly. Standby I've it barely uses a drop. 8 hours on critical low warning and it was still on. Turn off all the stupid functions that you never use and it lasts ages. Literally only need about 5 options selected max, loose all the air gesture stuff and bump things and it's brilliant. Puts Iphone 5's to shame that's for sure!