Despite following Tesla's Model S first respondents manual to the letter, firefighters from the Sacramento Metropolitan District still had to put out its 'spontaneously' flaming battery with 20 times the amount of water needed for an ICE vehicle. Tesla does warn in its instructions that up to 8,000 gallons may go towards extinguishing a burning EV.https://www.notebookcheck.net/Combusting-Model-S-battery-put-out-with-20x-the-usual-gallons-of-water-as-per-Tesla-s-EV-fire-manual.688237.0.html
It shouldn't be a surprise since batteries trigger a chain reaction when on fire. By the time one of the battery cell is fully extinguished, another one next to it will spark and light up the fire.