No, the XPSs don't have replaceable batteries either. The XPS 13 is a very tiny notebook/subnotebook, yet with full-size keyboard and all the performance of a larger notebook (it's very noticeably faster than my 2012 MacMini which also has an i7).

I guess battery mileage is mostly a function of the O/S and drivers, and your power settings and what you actually do on the notebook.

I have the Dell XPS 13 9350, bought used. When doing standard programming stuff (firefox + sublime + spotify, no CPU intensive tasks), I usually get around 8 hours of battery, so in practice it's never a problem.