Halon apparently, which is ineffective against lithium battery fires.
I'd rather not test this theory because of your cavalier attitude while I'm in a chair 40,000 ft over the ocean.
It's effective against the rest of the combustible material in the hold so ideally the fire remains contained to the battery.
Li-ion fires do not require external oxygen, the cathode decomposes to release its own oxygen gas during thermal runaway... fire extinguishers will not stop it.
Except you can't extingush a lithium cell fire because it has the oxydizer inside. Once you see one you'll understand. It's scary.