Apple will be released iPhone 6s with similar size battery, but with new hardware.
We know that Apple released new iOS 9 with new features. He fixed lots bags for biggest battery life for “old” iPhone 5 and iPhone 5s. It’s mean that new iPhone 6s on iOS 9 will have more battery life.
IPhone 6 owners claim that their smartphones work only one day, but analitycs claim that Apple must release iPhone 6s with two days battery life.