Simulator does not like the two parallel connected batteries but should work fine in vehicle.
Top lamp is starter motor at 300 amps. 10 amp current source is car alternator at idle speed and current output amperage tops about 1500 engine rpm.
Cut out switch on each battery to charge with alternator each battery with top battery to assist cold starts bottom battery being the run battery with the alternator after the engine is warmed up and running. Vertical switch at bottom goes to vehicle ignition and electrical systems.
Note output from the alternator goes through both cut out switches ( probably knife switches or able to handle high currents.
