I've been having this exact same issue after upgrading from 6.0.1 to 6.0.2 on my iPhone 5. I called Apple Support, and they fixed it for me. Here are the steps:
This is what Apple Support told me to do:
After doing this, my iPhone 5 with 6.0.2 has been working perfectly and battery levels are great (12 hours of standby only uses 1%).