This linked story has a good explanation of EV battery tech and how a component failure may have led to battery fires.
Koren news sources are citing anonymous sources claiming that Hyundai has found the cause of the battery fires causing both the Bolt and Hyundai recalls.
Battery chemistry and technology is difficult, more than most of us realize.
The rumors are that the car makers will end up replacing individual cells or entire battery banks. GM acknowledged earlier this week that they are making progress towards resolving the battery problem and implied that battery replacement might be an option.