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.
I can get rechargeable AAs in packs of 4 just around the corner from my house and therefore always have a few spares on hand instead of special ordering a unique battery that only works in a single device on the planet and only is available for purchase as long as they allow it. But I guess we can just throw it away in a few years instead and buy whatever new product they want to sell, as long as it comes with a charging cradle of course.