I had the exact same thing happen to me. Everything was fine then on a Wednesday night the battery started draining fast without any usage. Fast enough that my phone with zero usage of any kind drained completely in 4 1/2 hours. I did everything that people posted in this thread to help extend my battery life, which only helped a little bit. I was forced to carry my charger with me everywhere i went.
I finally gave in last Friday and signed on to Apple and went thru the support steps, which at the time was very unhelpful. There is no support option for people who's battery is draining. Anyway, I went thru the support and ended up having them send me a text message with a link for their diagnostic. I ended up running the diagnostic all 3 times before giving up on the online help and scheduled an appt for the genius bar at the Apple store 40 miles away.
The next day i noticed that my battery wasn't draining anymore. I tried to burn it up running videos etc. My phone went back to normal. I'm guessing that running the diagnostic 1 or more times must've reset something on the phone. My phone has worked perfectly for the past week.
note: After the diagnostic runs i did have 2 software updates AroundMe and TouchTunes. So, it is possible that one of them was the problem, but I really think that it was running the diagnostic that fixed my phone.