RedactedNarrative: Operator of vessel stated that he was cruising in a southerly direction outside of the break wall to Milwaukee Harbor by the main gap.  Operator stated that he began to smell smoke then the engine then died and he noticed heavy smoke from the area of the batteries, no visible flame.  Operator stated that he called 911.  Fire self extinguished prior to arrival of any first responders.  Operator did not use any extinguishment agent on fire.  Vessel is equipped with B1 portable extinguisher as well as a fixed halon system in engine compartment.  No injuries reported.  Vessel was toed back to south shore boat ramp by USCG Auxiliary vessel.  USCD did a post SAR boarding the found no violations.