I'm not sure why you are so reluctant to take the Leaf back to one of the dealers. Sure, they were lazy the first time, and simply reset the error codes, hoping they won't come back, but if you have documentation showing this is a constant issue, every time you charge, they will have to diagnose it properly. The manual has very explicit instructions on how to diagnose the P33ED error, and you have to insist that they run through it.
Check to see if there is a cell voltage which largely differ from the others.
As electriceddy suggested, there is most likely a malfunction inside one of the battery cells, and the manuals instructions are to find the bad cell and replace it. LeafSpy may help you find the defective cell, but they will still need to verify if with their Consult device.
< DTC/CIRCUIT DIAGNOSIS > [TYPE 1]
1. Select “DATA MONITOR” or “FFD”.
2. Check to see if there is a cell voltage which largely differ from the others.
Is there any abnormal cell?
YES >> Replace corresponding Module. Refer to EVB-152, "Exploded View".
NO >> GO TO 2.
2.DTC CONFIRMATION PROCEDURE OPERATION
1. If abnormal cell is not identified, perform DTC confirmation procedure. Refer to EVB-136, "DTC Logic".
2. Check cell voltage again using “DATA MONITOR” or “FFD” to identify malfunctioning cell.
>> Replace corresponding Module. Refer to EVB-159, "Exploded view".