Try it with 12 volts. If it runs and has power then it's probably 12 volts. I've had several trolling motors and used several. I've never seen one that was not 12 volts. I'm not saying that there is not one the is 24 volts though. A 24 volt one would be hard though not impossible to charge since outboards and inboards are 12 volt systems. P.S. Now I've done some more research and find that there are indeed 12, 24 and 36 volt trolling motors. What is the model number of the motor you have?