My immediate thoughts would be too many re-wrap rubbish being imported either knowingly or otherwise from China. Do we know what type of batterie? . The other would be as you said people using wrong batteries in their mods. I have seen reports of Ego II 's going off and also spare 18650's shorting when carried around in pockets with loose change, keys etc. I for one, if I need to take spare batteries with me use dedicated plastic battery boxes. They are not expensive. My thoughts would be on the lines stated above. In all my years of vaping I have had only one issue and that was caused by a defective internal mod circuitry. Now I point blank refuse to buy a vale that does not have a removable battery for charging.