There are standardized sizes for cylindrical Li-ion cells, and that's often what's inside battery packs. The majority of current mirrorless cameras, for example use battery packs that have two 18500 cells inside, but no two brands have compatible batteries. There are only bad reasons for the lack of compatibility.

I'd be happy if everything sized for it took standardized cylindrical Li-ion cells with protection circuits stuck on the ends. That's common for flashlights and rare for everything else.