I’ve been working with industrial electronics for over twenty years and have access to higher grade test equipment than the average end user so I did a quantitative analysis of the gray 9V batteries I received. Fortuitously, there was a (relatively) fresh proper yellow canned Duracell ProCell lying around the shop so I was able to add that to the comparison table. The basic analysis to take away is (with out dissecting the battery case) the cells appear to behave almost identically to the original yellow packaged ProCells, whereas the fresh plain “copper top” has a much higher internal resistance at load, the gray batteries match more closely with the yellow Duracell ProCell. The only thing I particularly don’t trust is the crimp quality of the top and bottom of the can (evident in the attached comparison photo). Weaker crimp quality could create a situation where alkaline cell leakage can more easily “burst” the battery can, and the crimp quality difference is significant. The unit with “DURALOCK” on it was extracted from a piece of test equipment for visual comparison and not used in the test due it’s age/wear.