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.
A couple of things, first no, I don't feel the latency of a Bluetooth controller. But also the steam controller will be able to pair to multiple devices, in one of the interviews one of the engineers said "The steam Machine has its own antena, but each controller comes with its own puck, we expect the common use case to be to plug that to your PC and use the steam controller in both devices"