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.
Hard pass on AA, but having a 21700 would be great: Epic battery life but it's still standardized and swappable. I'd even take 18650s.
This is where this all needs to go, swappable standard batteries like the 18650s being used and recharged in the device and replaced when the inevitable happens and they stop storing much charge. Batteries are consumable currently and devices without swappable ones are designed to fail within a few years.
My favorite controller is actually just a cheap 8bitDo 2c hall effect wired controller. Paid $20 but it works reliably and has a third shoulder button.
Wired connection is great for desktop, but the Steam controller is being advertised for use with the GabeCube, and nobody wants a 10 meter cable across the living room where the dog trips on it and yoinks your new $700 console from its desk
A single 18650 would have more capacity than the existing battery. That'd be dope. It is interesting how AAs and AAAs have a super common rechargeable standard, but the average person is not familiar with the lithium rechargeable standard.
I guess it's not a huge issue for controllers if you use them regularly, but the energy density on lithium-ion batteries is great, but the self-discharge isn't ideal. AA rechargeables are usually NiMH, and those do better on that front.
https://en.wikipedia.org/wiki/Self-discharge
I have lithium-ion 18650s in my high-power flashlight, but for devices that I leave around the house that don't really need a lot of energy density
think TV remotes or something
I think that it's probably sensible to use NiMH batteries.