I also use pololu electronic parts in my robot.
I a servo controller, USB-to-serial adapter. And once i connect the USB-to-serial adapter to the computer's COM port by USB cable, a red LED starts glowing. So if i understood your first question right, you wonder if you can run your system without any batteries attached to your controller, this is wrong. All the controller (USB-to-serial dapter/TtL) does is to take some minimized required power, to indicate that it's actually plugged in.