These can go up overheating cause inflammation of the battery and cause serious burns if they are in a mobile phone slipped into a pocket.
These defects appear on batteries whose manufacturing and quality standards are insufficient. For Anker, I tried unsuccessfully to whether it had been tested by certified laboratories like UL (Underwriter Laboratoiries), AFNOR, TUV.
Despite numerous exchanges of mail, I could not get a clear answer on quality testing and certifications that Anker had obtained with its products.
I bought two batteries for my HTC, they work well. However my fear remains.