Hodejo1 writes: Tesla has already put over 25,000 cars on the road with more to come and, presumably, most will still be running well past the 8-year battery warranty. What would happen if it is time to replace the battery pack on an old Model S or X and the cost is $25K? Simple, it would destroy the resale value of said cars, which would negatively affect the lease value of new Tesla automobiles. That’s a big part of the real reason why Tesla is building its own battery factory. They not only need to ensure enough supply for new cars, but they have to dramatically bring down the price of the replacement batteries low enough so owners of otherwise perfectly running old Teslas don’t just junk them. The Tesla Roadster was not a mass produced vehicle, so the cost of replacing its battery is $40K. The economies of scale of a gigafactory alone will drop battery costs dramatically. Heavy research could drop it further over the next decade or so. The good news is that if they do it right Tesla will have the replacement battery business to itself — without a gigafactory of their own non-OEM battery suppliers won’t be able to compete — which will bring more profits rather than headaches.