If you're curious, you can look around at the various battery troubleshooting threads over the years, especially the "I just got this great deal, but it doesn't work right..." or "too good to be true" broken battery threads, etc. Or the various analyses and reports (via video or photo/article) of the many counterfeit, fake, and recycled garbage cells out there.
The last is especially popular with the TGTBT pack sellers with 1million Ah packs the size of a paperback book

, where they recycle scrapped dead and damaged batteries of many kinds of cells into "new" packs with no testing, no matching of even cell chemistries/brands/models/etc. Most of those don't even try to hide the garbage cells under fake shrinkwrap labels like the Ultrafire and Trustfire and other *fire cellmakers do, becuase they've heatshrunk the whole mess into a battery pack you have to open up to check on, and they wouldn't honor a warranty even if they had one (many of them are flybynight and sell a bunch of stuff and disappear, probably starting up under new names somewhere else).
My favorites are ones that have been made of tiny batteries (sometimes even just capacitors) installed into cylindrical cells (usually 18650) and the rest of the weight made up with flour or some other material. No, it doesn't make any sense (but it must cost less to do that than buy real cells to resell)...but it's been done by various unscrupulous people around the world, for more than the decade-and-a-half that I've been here.