My iPhone 6 Plus battery is dying quickly, and also below 50% it drops to 0% within minutes, sometimes unexpectedly shutting down without the usual 20% and 10% warnings. My application use has stayed the same since I bought it new in Sept 2014. I took it into the Apple store twice, and both times their diagnostic tool showed the battery was in good condition. One of the Apple geniuses said it might be a software issue, so I restored the phone from DFU mode, and set it up as a new iPhone. I looked through all apps that used location, background updates, etc, and Even with hardly any apps on it the battery went from 50% to 20, 10, then 0 in a matter of a few minutes. I'm convinced it's the battery wear, on Apple's diagnostic it said I've had 500+ cycles. Could the fact I use the iPad charger all the time, and also my phone is almost always plugged in confuse the battery sensors or damage the battery? My Apple care ends in 20 days... 
