I would be interested to see if they were a first party charger and battery. Its very rare for genuine batteries to catch fire, but either with a third party charger or a third party replacement battery, not so much. (Former Apple Genius Bar tech.) All of the thermal issues I ran into with people's devices were from third party chargers. Except for the one time someone drove a staple through an iPhone battery that was in a box, that was quite the event.