from what i know about electricity, you can reduce voltage a helluvalot easier than increase voltage.. unless you figure something up that wires two batteries up to the winch alone, i think you'll have to get a new motor.. you could try shooting someone from the winch manufacturer and see if there's something you can remove/add to get the motor to run on 12 volts (as if it were made for 12 volts but they added a resistor or something to convert it to 24 volts)... just a thought.. good luck.