My iPhone 4s is running iOS 7.1.1 but it's absolutely KILLING my battery! 30 min of YouTube will drain at least 50% battery power and if I'm still using an app at 30% it will die. This phone is brand new, I literally bought it 5 days ago. Will updating to iOS 8.4.1 give me longer battery life? I've already reset apps and settings that drain the battery. Please help