Comment by shkkmo
Reconfiguring a battery pack with the same number of cells doesn't change the power contained in the pack. However lowering the voltage will lower your top speed (if not already artificially limited by the controller) and raising the ampacity of the pack may allow you to get more torque from the motor if you haven't saturated the motor and you change the controller settings to pull more amps from the battery.
Ah yes, DC motor speed is controlled by voltage. Glad to see Cunningham’s Law still holds true, thanks :)
I’m much more familiar with three-phase AC induction motors from my day job and the speed on those are (most commonly) controlled by adjusting the frequency with a variable frequency drive while maintaining the same voltage instead of directly controlling the voltage like on a DC motor.