If the fire did originate from the beacon, the cause didn't need to be internal to the beacon. If there were something wrong with the charging voltage, where it was a few volts higher than need be, it could definitely cause a battery, Lithium Ion, or not, to catch fire. A battery is charged at a higher voltage than the battery puts out. A 12 volt car battery might be charged at around 14 volts, but charge it with 20 volts, and it just might explode. I don't know what the supply/charging voltage was to the Honeywell beacon, but if it was supposed to be 30 volts and was 33 volts instead, adjusted wrong, or wrong for some other reason, it could cause a fire or explosion. So the fault not being with the beacon, but with the circuit supplying it.