"Use lots of water" is actually the best practice for extinguishing these kinds of fires.
First of all, there are actually parts of the car that are on fire (plastics, fabrics, etc.) and may spread fire to the surrounding environment. You need to extinguish those.
Secondly, the battery system is not "on fire" in the classical sense. It's undergoing a self-sustaining thermal runaway. You pour as much water as you can on it to remove heat and break the chain reaction.
> You pour as much water as you can on it to remove heat and break the chain reaction
...For long enough to remove the immediate danger of the fire to the surrounding people. Such a damaged fully charged battery will probably undergo thermal runaway and reignite repeatedly as soon as it stops being cooled. The best bet is to just keep the fire under control and not let it expand while it burns itself out.
First of all, there are actually parts of the car that are on fire (plastics, fabrics, etc.) and may spread fire to the surrounding environment. You need to extinguish those.
Secondly, the battery system is not "on fire" in the classical sense. It's undergoing a self-sustaining thermal runaway. You pour as much water as you can on it to remove heat and break the chain reaction.