Is this an autonomous (on-board powered) robot? Or does it have external (fixed) power? And are there other significant power requirements?
Obviously, if on-board powered, batteries are your only option, with some manner of a fixed charger for use when the robot is quiescent. If external, then the battery charger option will work.
One last question: If the robot is on-board powered, what will be the duty cycle, i.e., how long will the motor need full power?