...The 40 hours score means you will have to charge your Lumia Icon every 40 hours if you use it for an hour of 3G calls, a hour of web browsing and an hour of video playback each day. That’s far lower than we expected and, given the Lumia 1520 marvelous performance, it’s pretty obvious that it’s not the best the smartphone can manage. Nokia should act quickly to identify that issue that causes the battery drain and fix it as soon as possible....
Testing one phone is not statistically significant. They could have a lemon.