A friend in the automotive testing industry said that some EV batteries have small explosive devices inside them (similar to airbag inflation explosives), if an EV is in a significant accident the explosive goes off, effectively destroying the battery so it can't be used. If that didn't happen, the EV battery might be damaged without any visible evidence, re-used and then cause the exothermic reaction fire. So how many EV fires are caused by re-use of damaged batteries? I have no idea, but I would be aware of the issue if buying second-hand.
