The energy is used to drive the cars, replacing gasoline. I suspect your napkin math is probably calculating a different use case which is not the most common

The energy is used to drive the cars, replacing gasoline. I suspect your napkin math is probably calculating a different use case which is not the most common intended use case of car batteries, but rather, if even practical at all, only a trifling convenience, the scale of which will be lost in the noise when compared to actual driving usage. Again, what was your point?