I'm pessimistic regarding the effectiveness of any fire extinguisher you could have readily available in a vehicle - while safely secured. I have witnessed 5 police cars discharge the contents of theirs in a failed attempt to save a trapped and burning driver. Had no effect.
So... I'd appreciate observations from any trained fire fighters on the forum.
However, Tjin: "Insurance covers fires, not corrosion on electronics" isn't always the case... at least regarding MY policy (which I don't think is atypical). Coverage is present for incidental damage from fire-fighting efforts, too. YMMV