DC motors are used off of a battery or on a speed controller to vary the speed of the motor. These motors are better suited for lower speed operations. They maintain higher torque ratings as the speed is reduced.
We have 12V, 24V, 36V, 48V, 90V and 180V totally enclosed fan cooled motors available as well as DC controls. These are used in a variety of areas. The lower voltages, 12V-48V DC, are used when AC power is not available but battery power is available. 90V and 180V motors are typically used on DC drives to vary the output speed of the motor.