A great write up. I have one comment. On the point of a fire extinguisher, the only method that has proven effective is water to cool the thermal overheat condition. The smoke vents due to overheating and as each cell is affected by the heat from the initial cell failure and it vents. In general extinguishing agents are not effective, but doing anything to cool the battery will help. Typically, water works well.
It is best to focus on an air tight enclosure with venting overboard.
Hph 304CZ sold
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Retired Aerospace Engineer and A&P/IA