You can read all about it on iMore's sibling site, Android Central, but here's the gist:
[The] batteries built by Samsung SDI, referred to as Battery A, had a defect in the top right of the lithium ion grouping, and in some cells, caused fire through repeated charge and discharge. The batteries from Amperex, the Hong Kong-based facility that built the batteries for the second group of Note 7s, referred to as Battery B, had a defect in the top left portion of the cell that caused short circuits in a small number of units. In addition, Samsung says some of these batteries didn't have the necessary insulation to protect overheating from spreading to the rest of the battery in a short circuit scenario.
Didn't have the necessary insulation? Shudder. It's a nightmare scenario for any manufacturer and there's a lot to unpack about just how exactly this was allowed to happen, both originally and with the replacement devices.
My guess is it won't make much if any difference to Samsung or the Note brand long term anyway. This isn't a decade ago when even one major recall could seriously hurt a company and product. These days we don't really care about that kind of stuff anymore, and we've shown it time and again.
Check out the complete story and let me know what you think!