So I have the same issue as the OP -- coming from an iPhone, the battery life on this phone (as much as I love it) is relatively horrendous. Just a few minutes of web surfing will see the battery percentage drop a few percent. I noticed though (while vacationing abroad) that when the plane is on airplane mode the battery life is significantly improved - to the point where it's on par with my previous iPhone. But turning off Bluetooth, GPS, and apps that fetch data regularly now that I'm back in the States hasn't helped. It only seems to be airplane mode that does it.
Does this mean it has something to do with the phone's cell service? ie- it trying to reach towers nearby? I'm not a technical person at all, so this is just a wild guess...
I have noticed (from a little Googling) that some people say they have absolutely no issues with battery life, while others seem to be in the same boat as me. So does it have to do with the area you live in? I live/work in the middle of downtown Seattle, so I have a hard time understanding how this could be the issue, but I'm at a loss as to what else it could be, other than maybe just bad luck in receiving a faulty phone.