On impact, I would assume with an ICE based car, the fuel burns faster and there may be less of it since it could spread anywhere and everywhere once there is impact, it's a fluid.
Batteries on the other hand, I've seen a lithium ion battery for an RC car explode and burn, you are right, it's very fast, it's very intense, it smells nasty and even when we tried to throw soil over it, the smoke went through it like it was nothing, We were standing 6ft away from it and couldn't stand the smell, I don't know how firefighters manage even with all their equipment. So I can't even imagine how something to a scale of 1:1 would be like. No thanks.