This year's follow-up iPhone, the iPhone 6S, doesn't improve on that battery. And its newest features aren't as instantly game-changing, at least not on the surface. That's obvious: it's an S-year iPhone, and Apple always uses these subtle every-other-year S upgrades to tweak design and ramp up processor speeds. It's the phone for people who didn't get the iPhone 6 last year. And for the past few years, S phones have introduced evolutionary changes that seriously evolved the phone; the iPhone 4S added Siri, and the iPhone 5S debuted the Touch ID fingerprint sensor.