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 hear you. I agree requiring the whole back shell being removed to swap the battery is an oversight. Maybe they have a good reason for it, but doubt it. I'm not too worried about it considering, how often I'd have to swap in a new battery. I mean, even my used PS5 controller I bought 3 years ago, the battery works just as well as it did when I bought it. Still sucks compared to a PS4 controller, but that's a whole other issue. If I'm removing the backshell once every 3-5 years, I'm really not bothered in the least. It's just not an issue I care about.