ICOM NiMH and NiCd batteries have an internal fuse.
Lithium is an entirely different hazard. Used in the oil industry (because they will work up to 180C) they are sealed in their own explosion proof housing. I have seen what they can do, and it is nasty; I am not having one anywhere in an aircraft of mine.
As I said, battery technology is advancing and other, safer, technologies are coming.