Iphone 5 shuts down overnight since ios7.1 upgrade

This has happened twice since the 7.1 upgrade. This happened even after restoring my phone with itunes. I'm at a loss and Apple doesn't seem to care. Wow! I put it on the charger and go to bed. In the morning the alarm doesn't go off because the phone is off, completely off. I had to hold the on button for 10+ seconds to revive the phone.

Help anyone.