Gudcraft WG300 - I hooked it up to a new partially discharged 12 volt deep cycle battery at 12.74 VDC.
It's been hooked up for two weeks now and the battery voltage hasn't raised even a hundredth of a volt yet.
Not that the turbine hasn't been spinning, it has! It spins in a very mild wind; it just doesn't produce 12 volts until it is spinning so fast that you can't see the blades. I've had 15 MPH wind gusts with no charging. Tests I have run indicate it has to be spinning 4 to 5 revolutions per second to output 10 VDC.
That's about 250 RPM, and moving pretty quickly, above that speed the black dot Indicator I put on the center hub begins to blur and speed measurement becomes difficult. Fearing the unit was defective I took all the blades off and mounted it and spun it manually as fast as I could and managed to get it to 12 volts after a few tries, and finally up to 17 volts for a moment. So it is capable of putting out the proper voltage to charge a battery. Since I was only able to get it going that fast for a moment I was unable to measure the current output.
Today it's been windy all day and it's been spinning most of the time, but there has been no charging yet, save your money.
Update, today we had sustained 30 MPH winds with gusts up to 50MPH and the wind turbine was able to charge a single deep cycle battery from 12.75 volts up to 13.25 volts with a highest current of 0.7 amps. Since I'm not likely so see many days with these kind of winds, it falls very short of it's rated 300 watts or 25 amps. I still wouldn't recommend it to anyone. The wind speed was checked with a Lacross weather station anemometer. It rarely puts out 12 volts and so far never more than 1 amp. Actually today is the first time I was able to measure any current output at all. It's moving so fast today, I can't see the blades, they are just a blur.