[Ol' Dan Tucker]

Especially those items people by over the internet on Amazon, TEMU, EBAY, or other sites. Like the items that ship directly from China. These are typically the batteries causing these fires.

As a cost-cutting measure, Chi-com batteries omit the safety circuit that prevents overcharging and over-discharging, the usual cause of thermal runaway.

[OldHarbor]

Fake batteries.
Canon took that very serious . People would use fake batteries and their cameras were catching on fire.