i last edited 4:30 CST
if your rig uses an intellitec BIRD
not plugged into your shore AC...with new house batt installed and maybe using thick gloves, put house disconnect toggle to STORE and go disconnect and reconnect pos batt cable checking for sparks. if sparks, batt is not totally disconnected.
if no sparks, then set house disconnect to USE, then turn off every DC device you know about (don't miss stuff liks TV batwing amplifier), and repeat sparks check. if sparks, there is still a current draw somewhere.
regardless of any sparks, still in USE, plug in 30 amp shore and read house and engine batt voltages. your converter should be putting out over 13.2V measured at house batt, and if BIRD is working, its solenoid should go on and you should read same over 13.2V at engine batt (engine is off). if this happens, your AC power converter and BIRD & its solenoid are good as house is charging all things it should in USE and on shore AC
unplug shore AC and keep house batt in USE. check engine batt voltage - really best if 12.6 or more. turn on engine and alternator should send hi 13V or even over 14V to both batts (bidirectional charging). if alternator is still only 12.5V, it may have a loose fanbelt or some inner elec malfunction.
hope this helps in some way.