I think many people are mistaking the SVP fluctuations as a controller or voltage problem. The controller uses a microprocessor that simply sends timed pluses to the stepper motors. Most of the problems with with the SVP is the error in the worm and gears periodic error. The stepper motors are also plagued with backlash problems. All these things combined may make it seem like there are voltage fluctuations.
It certainly doesn't hurt to regulate the voltage to the controller but once battery voltage drops so far there will not be enough current for the motor to step and hold like steppers are supposed to. Just not enough current to produce the torque required.
JJ