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've had a couple of devices over the years that require one to unscrew a screw to open a cover to replace batteries. It's not that common, but I've certainly had them floating around.
In fact...I think that my analog multimeter does that, with a 9V battery.
goes to look
Yeah, Phillip's head screw. Though you only really need power on that thing for continuity testing, and some people might never even need to power it.