I've been running the latest Public Beta on both my iPhone 6 and Air 2, and i've been pretty impressed on both devices in terms of performance and battery optimization. I've always had pretty good battery life on my 6, and even better after I got an Apple Watch and have been using my phone a little less. At 8:30 PM, my phone battery is at 50% after being off the charger since 5:30 AM. I'm not using my phone at all times of the day and even then, I don't use it for many things that hog up the battery life (taking numerous photos, uploading them over an LTE connection, etc) so that definitely has much to do with why I get great battery life. But even still, I can't think why so many people complain about the battery life on the 6.