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 have an 8bitdo Pro2 that charges over USB-C and when the battery pack died of heavy use, you could just swap it out with rechargeable AAs and keep going. I’ve gotten over a year of additional use out of that controller now thanks to the support for AA’s.
I’m specifically not buying the Pro 3 because the battery isn’t replaceable.