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.
So ive got 3 kids and a large extended family. My kids are the youngest so we are constantly being given toys second hand. Looks like at the moment, ive got almost 50 toys that take batteries in some form. Most take 2, some take 4. 200 is admittedly a high end exaggeration. But ive changes batteries in hundreds of re-homed toys at this point and I have never come across a single set of recharable batteries.
When my kids grow out of them, we usually give them to someone else, as they were given to us.