I am getting about 8 hours when using the built-in screen, 10 when using external monitor. Not as good as Dell advertises, but better than I've seen on any laptop. My Macbook Air got 6-7 hours under similar conditions.

It may help to specify this kernel boot param in GRUB:

GRUB_CMDLINE_LINUX_DEFAULT="pcie_aspm=force"

Also you can try using TLP or similar Linux power management tools.

Sorry for reviving an older thread, but I installed TLP this morning, and it has made quite a difference. Before, I was getting roughly 8 hours per charge (i5, 1080 non-touch). Since installing TLP, my runtime estimates have jumped from 7-9 hours to 8-16 hours. I have been using my system on battery for 3.5 hours (same usage pattern as before) and still have 70% charge remaining, giving me a boost to a solid 11 hours estimated runtime. Nothing fancy, installed it and started it (sudo tlp start).

I have my machine set to do nothing when I close the lid, so it doesn't sleep or lock the computer. Since there is very little draw with the screen off, I hardly notice charge drop while on with the screen off vs. sleep. This saves me about 5 seconds each time I open the computer, as well as a lot of glitches from the sleep/wake cycle. I keep my screen brightness 5 ticks up from the bottom (is anyone else's lowest setting no backlight?)

I think Dell's advertised runtimes include the Power Companion, though the Windows 10 XPS 13 I tested in Staples was giving me 13 hour estimates with a webpage and internet radio open, screen about half brightness. It was also an i5 with the 1080 non-touch display.

OK, so starting at 90% charge, I've been running on battery for 7 hours, 32 minutes and have 36% charge left. Total runtime is estimated to be 12 hours, allowing for a few percent charge reserve left.

I have Firefox open with 13 tabs, a Windows VM for about 20 minutes total, WiFi on the entire time, and brightness 5 steps up from the lowest setting.

TLP definitely made a difference over stock Ubuntu 15.04. Before, my battery would've been flat already.