[Espeefan]

I'd be curious to see what kind of current this motor is drawing, under load, or when it stalls. That could tell you if it's a case of your battery pack not being able to supply enough current to the motor, when it needs it, or if the motor is simply underpowered for the application. Doing the math, at 41 watts (rated) and running on 12 volts, it should only draw 3 amps, which makes me think the motor is actually a little on the weak side.....