Performance of improved Ni/Fe electric vehicle batteries was measured at ambient temperatures of 0, 25, and 50 C for a range of overcharge levels, open-circuit stand times, and charge and discharge rates. Tests in which charges and discharges were performed at different battery operating temperatures showed that the discharge capacity of a Ni/Fe battery is directly related to its operating temperature, but its charge acceptance is decreased at 0 and 50 C by approx. 6% from that obtained at 25 C. The decline in battery efficiency at high temperatures is the result of increased self-discharge losses. In the first 0.5 h after charge, the Ah self-discharge loss at 50 C is twice (6%) that at 0 and 25 C (approx. 3%), corresponding to an increase in initial self-discharge rate from approx. 8 to 16 A. The increased self-discharge rate apparently occurs during the latter part of charging and, thereby, causes the 6% decline in charge acceptance. A decrease in battery efficiency also resulted at 50 C (6% coulombic and 4% energy efficiency loss) when the charge current was reduced from the 3-h to the 6-h rate. In comparison, low temperatures impact battery internal resistance and IR-free voltage more than high …