like, I bought a wireless Xbox 360 controller and all I needed to get it to work was one of those battery holders. Just works, lasts forever. The Steam Controller has the batteries in the grips which is nice (it doesn't have vibration motors anyways). My Minidisc player lasts days off of a single AA. It's just so convenient
Xbox 360 controllers also support those battery packs but afaik you have to charge those with a proprietary connector in the controller? wow that sounds annoying. This way I just pop in a fresh pair of batteries and I'm on my way