This paper explores certain key properties of lithium-ion batteries important for automotive applications. Long-term laboratory tests have been conducted to characterize these cells. The results address state-of-charge measurement and characterization, input-output charge efficiency, and needs and results with charge equalization. The results show that open-circuit voltage can provide a basis for state-of-charge measurement. High input-output energy storage efficiency is a key benefit of Li-ion technology - a vital performance parameter for hybrid vehicles. Charge equalization is an important consideration for Li-ion applications, and active equalization is needed to insure safe operation and deliver long life. Present commercial devices vary significantly among manufacturers.