I have an iPhone 6 that I received the day they came out two years ago. A few months back, the battery started going nuts. It would drop from 45% to 5% in an instant. Then would jump to 37% as soon as I plugged it in and then to 80%. Any video would instantly kill the battery even from a 90% charge. Took the phone to the nearby Apple Store and it passed their battery test at 90%. Told me to do a clean install which I did. Battery life continued to be a problem. Tried every trick to decrease use and finally gave up and walked into the store again. Clincher was when I went from full charge to 37% in 2 hours only sending texts and checking email. Another battery test - this time 88%. I said I wanted to replace the battery (I never got AppleCare). The sales person told me should would have to clear it with her manager. I asked "I'm paying $79 for this...right?" to which she replied "Yes, but I still need the manager to approve any battery swap with over 80%". Battery swapped, paid $79. Did not do anything else to iPhone (still on iOS 9). Battery life is perfect again. Slow decrease during the day (went from 100-87% with text/email/few apps between 9-5pm today). Moral of the story: the battery test in store is a joke and I no longer feel confident getting Apple Care to protect the battery since they only swap at 80% (which is an improvement from old 50% policy).