Regarding battery life, there are comments in macrumors forums from real users.
He also complains about dongles. I use my laptop with iPhone (sometimes) and with USB drives. Hardly an issue.
I'm a current 15" rMBP 2015 owner.
I tried the different models in the store. For those "on the go" the 13" is a nice "Air" replacement. I'm not certain I'd go with the touch bar version.
It is reasonable to keep up-to-date with Mac hardware if you use computers a lot. If things go wrong, it is far easier to take the laptop to the Genius Bar than options for other laptops.
EDIT: Comments on macforums claims 10+ hours.
http://forums.macrumors.com/threads/mbp-13-tb-with-2-50-batt...