And my point is, do not put a BMS into a case where a "thermal runaway" (Li-Ion) may happen...
First, according to the securaplane website, battery history is recorded by the
chargers - not the BMS co-located with the battery cells.
(We've been dispelling this myth every other day as someone who hasn't done due reading brings it up again and others in the same state accept it as fact.)
Next, once a cell enters thermal runaway, the job of the BMS has officially ended once it orders the final disconnect of the pack - there is nothing more it can do as the pack is headed for failure at that point.
(It's worth noting that this, too, apparently worked as advertised as there was a "drop to near zero" recorded on the batt of the ANA aircraft.)
Putting the BMS inside the battery case makes it easier to calibrate and more reliable. You are dealing with DC levels into the millivolts, and at these low voltages even the best connectors can add undesired and unpredictable resistance.
Since the BMS isn't recording history, nothing is really lost if it gets badly degraded when a battery does a thermal runaway.