UL is also not the be all and end all. You can build a UL certified pack with pretty shit cells. The most important aspect of a good battery is just use good quality cells that don't blow up.
LG produced a bad batch a few years ago and caused a bunch of fires, while other batteries in the same circumstance were perfectly fine.
Cell quality is one thing, but it is also possible and necessary to ensure that cell failures do not cause a thermal cascade that causes adjacent cells to fail. The whole "pack caught fire because of one cell" thing is optional. Ideally a catastrophic cell failure results in some venting of gas and a bunch of blown fuses at the cell interconnect level.
The level of increased risk depends on how many cells are in the battery. A large battery will need to be well-protected against cascading thermal runaway, but a battery with 2 or 3 cells there isn't much difference.
LG produced a bad batch a few years ago and caused a bunch of fires, while other batteries in the same circumstance were perfectly fine.