Further to my post 857:
http://www.pprune.org/7731615-post857.html
Three possible explanations for the 45A into the battery from 10:21:04:
a) Likely: that the charger commenced fast charging at about 0.7C
b) Improbable: APU bat bus was connected to a high current source such as Main bat bus.
c) Unlikely: Parasitic connection via small load such as nav lights. Such connection could not deliver 45A.
Thus it appears likely that the BMU has not detected the cell short and that the charger commenced fast charge, initiating the conflagration.
Detecting Cell short is difficult:
http://www.pprune.org/7679259-post500.html
(Note: since that post, it was confirmed that there are only 3 sub cells per cell)
What remains illusive, is the cause of the Cell short.