Hello: Just joined after just buying 2010 FFH with 72K on it. So far good except the BXT-67R in there now is over six years old and shows bad at autozone test in the parking lot. The car will "start" but overnight the voltage at the cigar lighter is 9.9V. Before I get autozone duralast replacement on their shelf, I need to know how to avoid a radio crash as I do not have any code numbers for the factory 6 CD changer AM FM Sirius with no navigation. Also, does main HVB need to be disconnected? Have no idea how to do that. Will stuff need recalibration afterward? Can I plug a 12V battery tender or backup device INTO the cigar port before any disconnect of the aux 12V? Would that eliminate these potential problems? Thank you.