I used to own the XPS 9550 (15", 1080p non-touch) and the battery life was around 6-7 hours with the Nvidia GPU disabled. I bought it used so it might have been even better new too.

That depends on use. For working on or reading papers, it's great: I've significantly cut down on the number of drafts and papers I print, as the screen's ppi is high enough that figures will appear at a similar resolution to what most researchers will have on their printers when adjusted to the correct size on the screen.