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.
The overwhelming shortsightedness of thinking highly polluting AA or AAA batteries are a better choice over a LiON solution pack because one needs to unscrew a couple of screws to replace it is completely unreasonable. AA or AAA are a stupid ask for a controller, it's unnecessary waste.
The overwhelming ignorance of rechargeable NiMH AA batteries is completely unreasonable. It's so nice when my Xbox One controllers die to just simply swap batteries, and throw the existing batteries on the charger. That said, you're not alone with that ignorance, those massive packs of single use AAs at Costco must sell to someone.
Heck, the Xbox One and newer controllers have replaceable battery packs that charge using the controller's USB port. You don't even have to swap them. All the advantages of a built-in battery, but when they crap out, it's like $15 and 30 seconds of work to replace them.
Only for so long as the manufacturer makes them. AAs don't have that problem.
But then you can replace them with AAs, and all you lose is the USB recharging. Best of both worlds.
If AAs are also an option then I have not complaints about the system.