I just noticed the significant draining three days ago. After charging it overnight, my iPhone 5 didn't show a full charge. I updated the software a few days ago. I had not added or changed any apps. I hope a fix comes out soon!
After doing multiple restore and lot of play i was able to narrow my heating and battery drain problem to calender sync with outlook. Turn off calender sync under exchange acount and my battery is back to normal usage and phone doesn't heat any more.