It's called the Nyko Power Pak with Charge Base. It's only $30, adds very little bulk to the system, and nearly doubles the battery life. I'm pretty sure I'll be snagging this when I pick up a 3DS. You can learn more about it Here.
Hey I might get this if I can find more reviews. I have a feeling it's a piece of shit. They should have just made the entire back part of the 3DS the battery instead of that little ass thing.
