I believe Replicator is saying that he doesn't want the entire robot to die simply because he doesn't have power to move the motors..
IE, he still wants it to send out video, regardless of motor battery life.
In which case, yes seperate batteries are the way to go. If you do use just 1 big battery once it dies, your done. Also it can be electrically noisy to use just one battery. On occasions even, when the big 20a motors(or whatever your using) hit on to max.. it could cause such a voltage drop it may reset your computer brain..
Of course if you do use a big one, simply attach proper sized capacitors to all of the motors(which shoudl have some anyways), and also to the brain. So that huge voltage drops won't effect it as often..