Most Lithium ion batteries for cameras are made of 2 cells (the round stuff that looks like a AA battery)
As far as I know, there are only 5 manufacturers of these Lithium Ion cells: 4 in China and 1 in Japan. Even Tesla doesn’t manufacture the Lithium Ion cells for its own car batteries, they use cylindrical Panasonic 18650 Lithium Ion cells.
The camera manufacturers like Canon, Nikon & Fuji “farm” out the manufacturing of their batteries to companies that specializes in the “battery business”. These companies assemble the various parts of the battery and package it according to the various requirements. The battery manufacturers do not make the battery cells, they manufacture the plastic, the casings and add the extra parts like cpu/sensors…
And now for the important part:
The Lithium Ion cells are graded from grade A, the highest quality, to grade C, the lowest quality.
Grade A cells are the better ones and they (are supposed to) conform to the UL1642 standard. The others don’t. When you buy a Canon, Nikon, Fuji… these cells have passed the UL1642 tests. It’s a quality assurance that is supposed to prevent the batteries from exploding and/or catching fire, or from draining when there is no usage, or chemical leaks….
The UL1642 standard for Lithium Ion batteries is not a guarantee. Ask Boeing about their Lithium Ion batteries catching fire with their 787 Dreamliners in 2013-2014.
The “copycat” batteries could be of grade A quality but without the actual UL1642 testing, it doesn’t matter since nobody will ever know. If there’s a problem, the reseller doesn’t really care, the reseller will exchange the battery.
The problem is that we have no idea what kind of cell are being used inside the “copycat/3rd party batteries” batteries.
BTW, I have been using NP-W126 from UpStart because they are sold by a local dealer. I’ve been very happy with them.
And no, their charge does not last as long as the Fuji OEM batteries. I would say that they last about 70% of the original Fujis but I think that paid $20 Canadian (at the time) for 2 batteries and I’m still using them today.