A few years back I was involved in doing some testing of camera batteries and their chargers. OEM batteries will often only charge on OEM chargers in the camera world. Third party batteries will often not charge on OEM chargers, so are sometimes sold with the third parties own charger.
So after a lot of testing we found some batteries and chargers were pretty good. Lasting almost as long as the OEM batteries with all the expected safety features.
However, there was some real dross. One battery, rated at a supposed 2480mah barely made 400. When we dismantled it we found a couple of cheap recycles lion cells inside with no protection whatsoever. The charger supplied with it was nothing more than a capacitive dropper. The terminals of the charger would give more than a bit of a tingle. These chargers and batteries were sold through Amazon at the time, fortunately they have gone now. They are still available on the bay of fleas.
That was a few years ago and I have spoken about it a few times online, sometimes with a bit of derision from people who want to justify their own choices. At the back end of last year I bumped into a photographer friend who I had not seen for a bit. He was on crutches and when I asked what had happened apparently a third party camera battery had exploded in his pocket. It took three surgeries to get him back on track from the resulting damage. He is getting better slowly and hopes to be walking unaided soon. Quite scary really but on the plus side it was only his leg and his love spuds escaped the burns.