Cozmo has an internal Lithium-ion battery that is charged using the included charging dock connected to a powered USB outlet.
Typical charging times for Cozmo are approximately 30 minutes, and will vary based upon the USB power source that you use.
When fully charged, that allows Cozmo to play for approximately 45 minutes. Actual playtime will vary based upon how you use Cozmo.
Cozmo's internal battery is not user-serviceable, but is covered by Anki's Limited Warranty.