Battery cells.
Something could indicate that some aircraft batteries are experiencing more frequent thermal events than consumer batteries. Why!, Size difference?
As others have already mentioned, protection of a battery cell against over current and over-voltage does not help if there is an internal fault in the cell.
As I see it, small cells have a significant lower probability of experiencing a thermal event, since they are more likely discharged before a fault in the foil (hotspot) reaches the autoignition temperature. And since they are small they can better conduct the heat from the hot-spot to the case of the cell.
A larger cell have:
1) More foil area, higher risk of faults in the foil → Higher probability of fire.
2) More foil area, more electrical energy to disparate in a fault. → Higher probability of fire.
3) Larger thermal resistance from fault location, to case. → Higher probability of fire.