Hi sergio85,
As I understand from your post you want to power both the Galileo and the Roomba iRobot from the same battery supply you listed right? Take a look at this link https://communities.intel.com/docs/DOC-21835 , it details the maximum current that can be drawn from a pin depending on the type of port used. Search for the port you are using and see the maximum current recommended by the document. Then do a test to see the amount of current drawn by the iRobot. Connect the board to the robot briefly and measure the amount of current using an ampmeter. If the current value is higher that the recommended by the document then continuous use of the board connected to the robot will likely damage your board.
Regards
Sergio