Do you have any more details on how you identified them as counterfeit? I guess they looked good enough at first glance, so the details must be quite subtle.
I’m not confident of my ability to identify counterfeit goods so I have greatly curtailed purchases from that well-known retailer that commingles inventory. Pretty much anything that might risk health or safety is something I’m scared to buy from them, which eliminates most items that use electricity - even in low voltages, as batteries can have hazardous failure modes.
The battery died very quickly so I was inspecting the "best by" date to see if I had a bad batch. I then compared it to some new batteries bought at a physical store. I noticed the font and some small details were subtly different. The base plate (opposite the terminals) was plastic with a fine texture on the real product, and simple black cardboard on the fake. The stamping and forming of the metal cover was more crude on the fake as well, and the trademark copper was duller.
However, there's no way I would have noticed any of these without a genuine comparison, especially if it was still in the wrapping.
This was for a smoke detector, so definitely a safety issue!
I’m not confident of my ability to identify counterfeit goods so I have greatly curtailed purchases from that well-known retailer that commingles inventory. Pretty much anything that might risk health or safety is something I’m scared to buy from them, which eliminates most items that use electricity - even in low voltages, as batteries can have hazardous failure modes.