Based on the description on their site, the controller includes a built-in battery: "8.39 Wh Li-ion battery, 35+ hours of gameplay... "
That was disappointing for me. Specially condidering the Steam Frame's controllers make use of AA batteries: "One replaceable AA battery per controller, 40hr battery life"
AA Batteries might not be as convenient to use, but being able to replace them is a great advantage. All my Xbox360 controllers still work fine, but none of my PS3' Dualshock 3s.
The official docking station could be used to recharge (rechargables) AA batteries so the functionality could remain the same.
It doesn't require "planning". You throw them in your bag and that's it. That's not a plan.
I usually don't have a bag with me. So it would need to go in my pocket, and I don't like those to be full.
If I have a bag, that means I'm either going to work (plenty of charging options) or on a trip. I've covered the latter case with the power bank.