Probably because Li-ion batteries don't have much of a memory effect and don't discharge on their own much. I don't think there is such a thing as a less flamm

Probably because Li-ion batteries don't have much of a memory effect and don't discharge on their own much. I don't think there is such a thing as a less flammable alternative, ultimately you're storing a lot of energy. Energy means potential for fire. Finally, I doubt these have the same chemistry as what they're putting in cars. There are a lot of Li-ion chemistries that are suited to different applications. It's more of a class of chemistries than a single specific one. Some Li-ion chemistries are cheaper and heavier than others but have longer lifetimes.