A not insubstantial amount, I'd predict.

(Anecdata) I had to prove that the work I did on a car (replacing the bumper) didn't cause a fire which burned down the garage and house it was in a week later.

That said, I do agree with your point that a brand new vehicle should not have these sorts of issues. Be interesting to see where the cause lay.

I'm not sure about brand new vehicles. Cars have a bathtub curve like anything else. I expect car fires are mostly very old or very new cars.

Just wondering but would insurance cover you in either case?

The burden of proof ought to be the opposite.

This is a very real threat albeit generally rare, of course.

As long as an electrical circuit has power it can begin to heat up wires or connectors due to bad contacts or worn threads, for example, even if the car is cold and has been sitting for days. In the lucky case there's a slow short that just drains the battery or burns out the wiring, stopping the generation of more heat. In the worst case the heat will melt something and provide a new, direct short to ground, which runs enough power through the wires to ignite something.

I have a garage for doing repairs and maintenance on my cars. Each time I park one of my vehicles (new or old) there I'll disconnect the battery negative cable and keep it disconnected unless I have to start the engine or connect to diagnostics. I have insurance, of course, but the idea of my shop burning down alone is enough of a deterrent that motivates me to do the small effort of disconnecting the battery. I really don't want to rebuild my shop and reacquire all my equipment because of a bad connector hidden inside the wiring harness somewhere in my car chose to fail.

And how many of those explode with enough force to send a garage door flying?

Large explosions from gasoline powered cars are indeed rare, but it's not uncommon for car fires to result in a number of smaller explosions that can be just as deadly, as pneumatic cylinders that operate a lot of hood and tailgate supports cook off an launch the rod inside out like a projectile.

Another fun failure mode of gas cars is that when the gas tank does finally fail, if the car is on any sort of a slope, you now have a stream of flaming gasoline to worry about...

I mean you need to compare that to a lithium fire which is its own kind of awful to deal with.

The reality is that current lithium batteries do have a very energetic failure mode - it’s not particularly common (because they’re engineered in such a way that a battery failure doesn’t trigger a fault in the casing) but when it does happen the immediate explosive force is much greater than for a gas tank. Also because physics lithium batteries do have a greater potential to simply “go wrong” when not in active use.

That said it is obvious electric cars are the future - I just hope we can do better than the current battery tech, the power density is way down on gasoline and that means the batteries are huge, and therefore weigh enough to impact overall car efficiency.

Sure, my point is just that gasoline isn't all sunshine and rainbows.

Large energy capacity batteries, and lithium specifically, definitely pose some new and "interesting" challenges. I'm optimistic though. Gas tanks are as safe as they are today because of several decades of safety-focused engineering and iteration.

If you gave me a choice between an ICE or an EV fire, I'm absolutely going to choose the gasoline, but that's just because it's a very mature technology, with well understood practices for dealing with them. I'd be surprised if I have the same answer in 10 years time though.