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.
that's honestly the best move, even if it is more expensive it's totally worth it.
Hell, these corporations could even make more money selling you additional packs you could swap if you didn't want to use rechargeable AAs. It needs to be the standard, it would keep so many controllers out of landfills when their batteries go bad. Microsoft kind of does this with the standard Xbox controllers, but in typical Microsoft fashion they make your first rechargeable pack a separate purchase. I'd still way rather have that than the built in batteries though.