Which approach is "more realistic" depends on whether you are evaluating the decision between an electric car and a gas car at the margin, or not. If it's you

Which approach is "more realistic" depends on whether you are evaluating the decision between an electric car and a gas car at the margin, or not. If it's you as a consumer buying the next car to be produced, then it is entirely appropriate to compare it that way, because your single purchase will not change the entire life cycle.