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.
Classy, tfw when people who don't understand energy density and recharge cycle count, pitch in. Moar stuff, moar polution. Don't know how to lower the bar further on the point.
edit: love the US defaultism, I guess I shouldn't expect much...
We're talking about a controller here, not a smartphone. Rechargeable AAs are more than capable enough for these kind of devices. Not everything needs to have the energy density that Li-ion batteries provide.