The UBoost is the traditional add-on battery pack, attaching to the back of the GamePad to extend playtime "upwards of 10 hours." It has a built-in kickstand, replacing the dock as a stand – though the dock still charges the GamePad with the device plugged in. The Charge Base Pro charges two Pro Controllers simultaneously.
Other accessories include replacement charging stands and AC adapters for GamePads, and the Charge Link, a handy USB charging cable. You can use the Wii U (or any other powered USB device) to charge the Wii U's controller. What a novel idea!
The Charge Link cable is out now for $15, while everything else is due sometime this year.