I found one of the threads about module replacement and indeed, it seems like it is a single cell blowing in a module, causing massive loss of capacity and weird Voltage imbalance errors, leading to Turtle mode and other issues.
Two certified techs from Nissan are required to work on replacing a module, so it took weeks to arrange for all the logistics and I doubt that this has any benefit over simply replacing a pack by Nissan. Leaf Spy can easily detect these failures and diagnose them from the displayed cell voltages - let alone from the DTC error reports.
NOTE that early (2011-2012 packs were bolted shut with a solid rubber gasket clamped between the two halves of the shell, so you can easily open and re-close it.
Since 2013 the shell is glued shut. I have serious doubt that anyone from Nissan will try to open such a shell, it is a major headache and leads always to damage to the shell. I have only glued one pack back shut and I will have to see how it holds up over time, it is on my private vehicle.
Was interesting to read the thread about the module replacement and the issues encountered.
I have started to put 2 full Leaf packs (96 modules total) into my EV truck together with 2 Leaf BMS units.
That will be an interesting experiment and I hope to get close to 100 miles range.
I want to modify a "CANary" to display the info from 2 BMS units on the 2 displays as well as give the over/under charge protections.
We'll see if we can figure out the interface to the truck for the BMS. The packs themselves are not a problem,
though I need to re-configure them so it is a lot of cutting of metal and slicing of orange bus bar and sense wiring protection plastic.
What I did learn was that I need to keep all cells from a pack together to allow the BMS to keep them together, so I will make two
independent strings of 48 modules (maintain the two original packs) which only get paralleled when charging and driving.