Somewhat off the subject, but still related.
Your Parallax 7345 converter is a single stage converter. The output remains at 13.8v, high enough to boil the battery fluid but not high enough to charge the battery very fast. Modern converters are 3-4 stage. They start out with a voltage high enough to rapidly charge the battery then reduce the voltage to lower levels to finish the charge and maintain the battery charge.
You might consider replacing your converter with a Progressive Dynamics series 4600 or 9200 or similar converter if you are planning to do much off grid camping.