The main difference in hybrid and electric cars is not in the regenerative braking systems, but in the ways they attain the remainder of the energy required to run the car. Hybrid vehicles have a gasoline engine in addition to the electric motor that uses the regenerative braking system. This engine can be used to aid the electric motor in powering the car or even in charging the batteries. This allows hybrid cars to operate without the necessity of stopping to "charge." Electric cars, however, still need to be periodically recharged. Without the presence of a gasoline engine, these cars are unable to operate when there batteries run low, and although they too can charge their batteries through regenerative braking systems while in motion and in general when stopped, these methods are not sufficient to eliminate the need for separate recharging of the batteries.