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 absolutely would have preferred to use my existing rechargeable AA collection. I have them in a tray next to a charger on my desk, the charger shows the condition of the battery and swaps are fast, no need for disassembly and risking breaking plastic clips on the shell like happens every time I have opened a ps4 controller to replace not the battery but the charging board.