Same four* suppliers actually, just about every rechargeable embedded battery is made by Panasonic, Sanyo, LG, or Samsung.
Most common type/size is the 18650, used in everything from drills, powerbanks, to Teslas. Second most common type is the 21700.
A "scientific" test isn't even necessary, just tear down the battery pack, see what cell they put in there, and read the spec sheet. The big 4 battery makers will sell you a whole range of batteries in that size with varying mAh/Amp.
Googling teardowns, I found a Black & Decker 1.5A MAX Lithium simply uses a bunch of Sanyo UR18650W2 (1500mAh rated at 18A) cells, while a teardown of a Dewalt pack shows they used the more expensive LG HB4s (1500mAh rated at 30A).
There literally no reason they can't use the better cells in the Black & Decker, other than they're building it to a cheaper price point. The fact that they're built in the same factory is besides the point.