You don't want to breathe either, but the answer generally is battery fires which can produce extremely toxic gas like hydrogen flouride

https://m.youtube.com/watch?v=lADLvwAJs-c

https://en.wikipedia.org/wiki/Hydrogen_fluoride

Honestly no idea. But after receiving multiple fire trainings and talking to trained firemen, I have to say that all else being equal (and gun to the head because I actually want neither) I'll take a diesel fire over a battery fire any day.

A lot of dangerous fumes come from the other material burning around the source. And at 1000C plenty of neighboring stuff decides to burn.