There are fire extinguishers and smoke detectors in the holds of aircraft.

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.

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.