Hi Jan,
Are the blades spinning pretty fast? You mentioned the wind is blowing, so we assume they are. I don't think I've ever heard of a 12v treadmill motor. They are usually over 100 volts. Are you sure its just not a typical 12volt permenent magnet DC motor. If it is, those are all very high rpm motors and will not reach 'cut-in' voltage(12v) even for a 12volt battery. Most only get around 3 volts. If you could give more info. about the motor(name, rpm ,amps,etc) , many here can help more.
Your not losing anything in your short 10 foot wire, thats for sure.