The faults classified as permanent are emissions related faults in the PCM, unlikely to find a PCM fault that leads to a battery discharge diagnosis. There are several computers in the vehicle with non-volatile memory, but the faults detected by those computers generally won’t explain why the battery discharged.
Those insurance company dongles that connect to the data link connector can cause a drain on the battery. A device that proves you don’t drive the vehicle often can contribute to a dead battery. The tech will remove the dongle to connect the scan tool for a computer scan and the problem is temporarily gone, until the customer reconnects the dongle.