we have  a   BOOSTER  charger   that has  a   BOOST 6v  and  regular charge  12v  as the same setting---    and  that is  possible..  from an engineering  stand point..      
 since    volts times  amps  =  Volts times  amps =  power 

and   that is what  the generator  aplies too...  volts  times amps..