Yes the model year and history of the car would have been an important detail to reveal in the first post.
The Cell Monitoring Unit boards in the pack get powered from both the 12V battery and the modules to which they are attached; i suspect that the cells are drained themselves while sitting for so long.
Relay and harness connector contact surfaces may be oxidized from sitting unused for a long time; wiring may have rodent damage, etc. It is a tedious task to check and verify all the wiring, relays, fuses, connectors, but that is what will be needed to troubleshoot electrical problems.
Does the obdlink give you the cell voltages?