I think this is a huge problem with Chinese mass production e-cigs that's going to catch up with vaping comunity at some point. I hear a report about one of these fires monthly it seems (I heard about one last month). I personally have friend it happend to twice (due to a faulty charger).
Having gone through and tested a number of generic eGo chargers, I can see where the primary fault lies. The chargers they are selling to use with e-cigs are wholly inadequate. After scoring zero out of twenty generic eGo chargers within spec, I finally decided, "screw it" and designed one myself that conforms to voltage and current specs tightly. I did later get a hold of some genuine Joyetech chargers and all of those I ordered were within spec. These generic e-cig chargers are a huge hazard, it's scary really.
Another issue is the way e-cig chargers work. Normal operation for a Li-Ion charger is to disconnect from the battery when current drops below a minimum threshold in CVM (constant voltage mode). This signifies the end of the charge cycle. e-Cig chargers do not do this. They remain connected pushing current into the the cell as long as there's any voltage differential until the battery unit is physically removed from the charger. Current sensing only changes the light from red to green but does not disconnect the cell. Absolutely do not leave one of these e-cigs connected to the charger for long periods after the charge is complete.
The other thing that makes the issue worse is the cells used in the battery units. They have none of the safety features you find in a round cell like an 18650 or 18350. They're highly flammable so any fault has a high likelyhood of causing a fire.
These factors make using a mass production Chinese e-cig risky at best. Any Li-Ion battery is highly sensitive to faulty charging and for a Chinese mass production e-cig, the result is likely a battery fire.
