NO RV Genset charges any battery. Gensets have NO charging system at all. What the genset does is supply 120 power to the onboard COACH Converter or Inverter/charger, whichever you have, and THAT appliance charges the coach batteries ONLY. Your Emergency BOOST, requires the COACH batteries to be charged. The BOOST button is activated by the Coach battery 12 volt signal. It then merges the coach and Chassis batteries by a solenoid to supply power to start the engine. Odds are, as another posted stated, you had a temp bad connection on the engine starter/solenoid system. Doug