I do very similar things that you mention and in the same work-setting (indeed, if I take the ManUnited avatar seriously, I am even in the same country as you may be in - though it has not yet been released there - I bought mine overseas) that you refer to. I use the SP3 (i5/ 4GB version) and find myself getting usually 8 hours of battery life.
Unlike what dman27 points out, the max level of brightness that I can handle is not more than 40-45%. As for notifications - I have mail notifications turned on polling two email accounts (of which one is gmail and the other is my univ. email) as mails come in. My documents are on OneDrive (with the off-line capability turned on). I also use Office 365 extensively with Word and PPT seeing the most use. I have a few other notifications turned on - Flipboard, the News App and a few (but not many) other apps. Wifi is always on and so is BT (as I use a mouse). Around twice or thrice a week I use Skype (each Skype session lasts about an hour or so). I use OneNote (MUI version) with the Pen. I also use the Pen to mark/ comment on student work, to annotate any texts that I may be reading (and I am reading all the time!) and to take notes for the sometimes endless meetings that I have to attend (both at the student and the department/ faculty/ university management level). I do all of the above 5 days a week (usually!). On weekends, the SP3 sees a little less use since I spend most of my weekends writing my papers, research applications and working on my (hopefully) forthcoming books.
Given the above and when compared with your use and experience, honestly, I can't explain the discrepancy.