Impact of regenerative braking on battery performance and energy cost in electric vehicles in urban driving patterns

Studies on the effects of regenerative braking on battery performance indicate that an electric vehicle designed to return an important fraction of its kinetic energy to the battery during deceleration and braking can significantly extend the range of the electric vehicle. Achieving the equivalent range in a vehicle without regenerative braking would require a battery having a higher energy density. The battery itself exhibits an effective energy recovery capability. This capability provides that energy, which would otherwise be irreversibly lost to heat and wear of the vehicle brakes, can be efficiently recovered by the battery, stored, and made available for subsequent use. Consequently, the net energy required from the battery per mile of vehicle travel is reduced, as is the energy required at the wall plug to charge the battery. Therefore, for a given vehicle range, the actual depth-of-discharge to which the battery is subjected is less with regenerative braking, and an increase in battery cycle life should result. Data are presented to support these observations on improved lead-acid, nickel/iron and nickel/zinc batteries being developed by private industry under DOE contracts managed by Argonne National Laboratory.