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.
This is a very good point. If it's as easy to replace as AA and it lasts longer, it's just better all around.
A few problems: it will still use rare earth metals, and those are a hot political topic right now with China restricting them
The fact that AAs are eternal. Who knows if this specific battery will still be available in 10 years.
Also, the small problem of you can't just buy a new one at Walmart. It is small, but out of sight, out of mind, and out of the public consciousness.
Problems with Li-ion itself, I suppose. What we really need is a standardized small rectangle form factor since Li-ion is just more efficient in that shape.
If there's a market for it, replacements will be made. You can buy a replacement PS5 battery for $5. You can also buy a iPhone 4 battery (still). LiPos are quite easy to make (geopolitics aside) so making one that fits is not hard at all.
The PS5 battery has a plug, if the Steam Controller is like that (probably is), the only tool required is a screwdriver, which seems like a great tradeoff to replace the battery every 5+ years instead of every week or two, and being able to recharge it easily and quickly.
Worst case scenario you have to use a generic battery that is about the right size instead of a perfect fit. Maybe a little less battery life but it's still more than enough anyway.