In the light of power system decarbonization, electric vehicles are becoming an important tool to bridge the gap between traditional and low- carbon power systems. If aggregated, electric vehicle’s fleet can provide flexibility to system operator. Recent literature defines aggregators as electric vehicle charger aggregators which collides with the conventional way of observing electric vehicles, as stationary chargers with connected loads/vehicles. This paper observes them as mobile batteries, not chargers. Therefore, new concept of electric vehicle battery aggregator has been defined which exploits their mobility. Battery aggregator has more information about vehicle’s behavior and can maximize their flexibility provision regardless when and where they charge. New concept brings benefits to all system participants from electric vehicle owners, aggregators, and system operators to society altogether.