Sad to hear all the bad battery reports... Stock, this phone beats my 930 under similar usage (and that's with Windows Hello enabled). I should point out my usage is high on new features (Hey Cortana, Band 2 Bluetooth always connected), and I've enabled glance on the XL, but I keep the XL screen at 25% (though maddeningly it always resets to 50% after restart). Unlike the 930, a cellular data connection drains the battery faster than WiFi on the 950XL, which might be because I'm on LTE (my 930 only gets 3G here).
When I first got the XL I noticed the battery lost power during standby - I'd leave the phone in my pocket at 78%, and take it out an hour later to see 73%. Since the update to .29, the standby drain seems to be gone (it's only been a day so we'll see how it looks by this weekend), so I'd suggest everyone grab the .29 update.
But as everyone noticed, the biggest drain is the display, so the easiest thing to go after is screen brightness. And make sure you turn off the screen as soon as you're done with it.