smelly catalytic converter?

Well like I stated, a quick simple test of the battery voltage at rest vs running no load vs running full load should help you pinpoint it. The second battery is to maintain battery voltage while cranking in a hard start cold morning. The number one starter killer is low battery voltage high load. The amperage goes through the roof. Do yourself a favor, charge and test the second battery if its good hook er up. Your starter will last a lifetime longer.