9 volt battery not being able to power motor driver
It is likely not a question of the voltage being &quot;big enough&quot;. You do need to feed the correct voltage to your robot, but max current and capacity are also very important.
Those &quot;9V transistor batteries&quot; have very low peak current and very low total power capacity (measured in milliamp-hours, or mAh.) They are not up to the job of powering motors. You could easily drain a 9V battery like that in 15 minutes, much less a week.
You should connect 6 D cells in series, and use that instead. That would give you enough peak current and total capacity for your robot.