Joy, what you describe (runs for 10 seconds and then turns off) sounds like
you are not getting ignition, that second sound you hear when the combustion
chamber actually lights off.  So the Propex is shutting down because of no
ignition.  I'vehad that with a low battery.  Check the voltage on the aux
battery if you can.  Or start the engine and give the Propex a try with the
alternator providing electricity to the aux battery (assuming you have the
standard relay setup between the starting battery and the aux)