Q: iPhone 6 shut off unexpected

If your iOS device restarts or displays the Apple logo unexpectedly - Apple Support

You may need to calibrate your iPhone's battery.

Use your iPhone until it's completely dead then charge it to 100% (do not use your iPhone while its charging). The hold the home button and power button. Your phone will appear off however you must keep holding the buttons down until you see an Apple logo appear.

It is recommended that you do a full charge cycle each week. You should use the iPhone until its battery indicator shows that the battery charge level is below 20%, then charge the iPhone fully (do not use your iPhone while its charging.

Did this and still have the same problem. My phone will say I have anywhere from 20-37% battery life left, If I go to use Siri the phone will shut off and not turn back on until I plug it into a power source. It will then take 5-10 minutes for the white apple screen to appear and the battery life will then say 50%. If I try again to use Siri the same thing happens.

this is BS