Seeing I'm a bit old to be racing cars through our local shopping strip, it was fortunate that I slowed down to think about the expression like a bat out of hell.
I don't see why bats would be racing out of hell. Surely they should hang around down there to bother the troubled lost souls. And the word hell? Sounds like the German word Höhle, which means cave.
An interesting discussion at The Phrase Finder points out that bats flit rather than speeding around; but a mass of bats flying out of a cave together might seem fast.
The writers also point out that the expression was given new life by the Meatloaf song in the 1970s. I'm sure that song is the reason the phrase has stayed in my vocabulary.
Word Detective says:
Bats also are amazing aerial acrobats, flying swiftly through the night using only their natural sonar (high-pitched squeaks) for guidance. The bat's flight is so quick and erratic that when aviators during World War I needed a simile for flying at top speed, the bat was a logical choice "Like a bat out of hell" first appeared in print in 1921, but is said to have been in common usage several years earlier. The "out of hell" part was tacked on purely for added color, and probably refers to the bat being "from hell," not necessarily trying to leave hell.
I guess the meaning does relate to bats coming out of or from hell, but I prefer my image of bats streaming out of a cave as the sun sinks in the west behind a bank of black clouds.