Or, more accurately, the shell. An EV fire happen on the cellular level, by which I mean within the battery’s pouches or cylindrical cells. But those are housed inside the battery’s casing. So, while the inferno rages inside the housing, fire fighters are only cooling the outside. Hence why so much water is needed. Or why the darned things keep reigniting. You’re never directly attacking the heat source.
There are many lessons to be learned here, but one of the most logical would be that it probably behooves us to engineer electric-vehicle crashworthiness significantly better than that of ICE-powered vehicles. EV fires are, again, rare, but considering their tenacity, reducing them even further would seem a priority. Insurance companies, as recently discussed, are so worried about the dangers of damaged batteries that they are writing off EVs if the battery’s outer casing is but scratched.