According to Apple's new battery test, that's normal. My iPhone 5S has been doing the exact same. If it's windy outside, It'll die even at 70% battery.
Did you ever find a fix for your phone?
I still had guarantee left and left it for maintenence at my local authorized retailer who ran the new official Apple battery diagnostic thingy, which eventually stated there's nothing wrong with my battery?!
Eventually they proposed that we'd lie that the phone has antenna issues and send it to maintenence. (WTF?!) Apparently in most cases you just get a new phone.
Did you ever find a fix for your phone?
I still had guarantee left and left it for maintenence at my local authorized retailer who ran the new official Apple battery diagnostic thingy, which eventually stated there's nothing wrong with my battery?!
Eventually they proposed that we'd lie that the phone has antenna issues and send it to maintenence. (WTF?!) Apparently in most cases you just get a new phone.