13.6VDC is the output of your converter, not the actual battery voltage. To get the actual battery voltage, disconnect from shore power (or place the use/store/ switch in the 'store' position and let the batteries rest for a few hours. Then take a reading at the batteries with a volt meter.
Lew Farber...RVIA Certified Master Tech...ABYC Certified Master Marine Electrician
SOLAR TECH ENERGY SYSTEMS, INC.
AM SOLAR ...MAGNUM…VICTRON ENERGY...LITHIUM & LIFELINE BATTERIES…MARINE REFRIGERATION