You have some more firm facts to work from, so best to use that. Let’s use the Teslas figure at 500km, and a charge cost of $20, from easy figures to work with. Take a decently efficient petrol car that averages 5l/100km, it will require 25l of petrol to get the tesla’s 500km.esla Australia adds that it doesn’t expect its users to be filling their batteries up from absolutely empty every single night, which means that the $20 estimate is a theoretical maximum cost. Most times, it will be cheaper than that.