Reviews tend to show the iPhone 6 gets quite good battery life - I'm surprised your S4 runs out so quickly, but of course it depends on how you use it.
Ag i don't know, this phone has only given me grief and has been a huge disappointment, When i got the phone the battery lasted a day, i was quite happy about that since that was my main issue with my old Iphone5. About 2 weeks back i go to a party and we use my phone for the music, the battery goes for a good 10 hours (which was good), and at about 7 that night it died, so one of my friends who also has a S4 offered to borrow me his battery since the party has to go on...end of the night we swopped back and since then, the phone is farked, it gets extremely hot (no swelling), i even bought a new battery, same issue....
I'm so tired struggling with this phone, i just want to get an iPhone and have a phone that works again.