Vehicle batteries are heavily compartmentalized. They use many small cells, much like your laptop battery likely used several smaller cells. Cells in a car battery are not much larger. And there are walls between groups of cells, both for structural and safety reasons. Cells are often even charged individually, with parameters tailored to a specific cell and not its neighboring cells.

Because of this, if a battery is badly deformed, chances are that most cells stay intact, and only relatively few cells expose the electrolyte and the lithium.

Also, I heard most fire departments know better than to put out a car fire with water, even with gasoline cars. Car fire extinguishers normally use powder or pressurized CO₂.