In the right corner it's....Sir Gawain! He is nephew to King Arthur, and an honorable knight of Arthur's Round Table. He is very popular with the ladies, and quite charming. He is loyal to his king and queen and keeps his promises.
To charge the battery, the alternator voltage output has to exceed a minimum charging voltage. This minimum charging voltage is 13.8 volts dc across the battery terminals, or at the output of the alternator. A single lead-acid cell starts to charge at anything over 2.25 volts.ince a 12 volt battery has six cells, any 12 volt lead-acid battery needs at least 13.8 volts to start to charge. This voltage will be enough to fully charge or maintain the battery on a trickle charge, but charging time will be very long at 13.8 volts.
BAD idea indeed, the alternator will require power to generate the magnetic field for the rotor, this power may run as high as 100 -- 160 watts depending on size of the unit, also the RPM needs to be quite high unless you place a RPM multiplier to produce the 2000+ RPM needed to attain the desired power.