I had a look at reviews such as windows central, fsptopers, cbutters tech, mobile tech review, Linus tech tips on battery life with edge, engadget and Verge.
The average number I'm hearing more and more is around the 8 hour mark with "normal use". Extremes seem to last between at 2,5 hours more maximum cpu loading for extended periods and 16 hours in maximum battery saving settings possible. In all a full day battery life is achievable. There seem clues that the i5 fanless model performs slightly better in terms of battery life. 9 hours of daily battery life is apparently realistically achievable. Battery life is overall better than the surface pro 4.
I can recommend watching Linus Tech tips recent videos on improving battery life in windows and perfomance of browsers on windows 10, and fstoppers and cubtters test of the windows devices for more info and insights.