The only way of making electrically powered vehicles practicable is to have their batteries interchangeable (charged for discharged) at drive-through service stations, requiring less time than it takes to refuel a conventional vehicle. The fit, form and function of all batteries would have to be the same, although they could be stacked to suit the size of the vehicle, charging stations would have to hold sufficient batteries to meet demand, charged from off-peak power (which could be controlled by a nationwide data-bus, automatically switching off stations if the mains frequency drops below 49.999Hz) using power that would otherwise be wasted. As the power would be free, drivers would only have to pay a battery's depreciation cost plus a nominal charge towards the network. Although the external fit and form of the batteries wouldn't change, what was inside could be improved as technology advances.