I expect a lot of the fires are from batteries that are basically fraudulent products. If you randomly buy cells on alibaba, you will eventually get some that have lower capacity cells inside. But it doesn't even have to be quite that bad of a scam before the cells will give you problems. Sony had laptop fires, it's not like it's really something you can just decide to make without some technical expertise. And a lot of people don't have a good charger either, so in combination with borderline cells that's a fire waiting to happen. I feel fairly confident that my wife's Shimano battery is safe, but it's a little bit of a worry.