I'm not sure if I need a new battery or just to reset my phone but it's been randomly shutting down when it hits between 20% and 10% Anyone else have this problem??
Try "resetting all settings" first and then see how things go. If they improve, great, if not, try restoring the device and setting it up as new. If things continue tone the same, make a Genius Bar appointment with the nearest Apple Store to have them diagnose and fix the problem for you.
I've had the same issue. When my iphone 6 dips below 20% the percent charge left drops randomly without regard to usage, and occasionally turns off. Will try Just_Me_D's suggestion later tonight.