My headlights were going dim when the rear window defog was put on or the air was put on high. I took it to the dealer. They confirmed my issue and according to my repair ticket "With loads on only charging at 12.8V. Also inspected and found ground cable for battery starting to come undone and corrodded. Defective ground cable caused altonater to stop charging. Replaced altonater and ground cable for battery. Rechecked charging system. Charging at 13.6V at idle with loads on." However the lights still dim somewhat when the air conditioning is placed on high. Is this a problem? What should be done now?