Get an old bike wheel and an alternator. Rig the wheel like a wind mill. Fix the alt so the pully lines up with the wheel. Make a "fan belt" and connect the wheel to tha alt. Place in windy spot and make sure it spins. If it does you just simulated the conditions under you hood. Stop it from spinning for a second, connect your battery "+ to +, - to -". And let it go for a while. I have done this to power a radio for shits and giggles. If the Alt isn't internally regulated then of course you will need the correct regulator. No shit this will charge your battery without much effort.