Low temperature electrical performance characteristics of A&T, Moli, and Panasonic 18650 Li-ion cells are described. Ragone plots of energy and power data of the cells for different temperatures from 25 degreesC to -40 degreesC are compared. Although the electrical performance of these cells at and around room temperature is respectable, at temperatures below 0 degreesC the performance is poor. For example, the delivered power and energy densities of the Panasonic cells at 25 degreesC are similar to 800 W l(-1) and similar to 100 Wh l(-1), respectively, and those at -40 degreesC are < 10 W l(-1) and similar to5 Wh l(-1). To identify the source for this poor performance at subambient temperatures, both two- and three-electrode impedance studies were made on these cells. The two-electrode impedance data suggests that the cell ohmic resistance remains nearly constant from 25 to -20 degreesC but increases modestly at -40 degreesC while the overall cell impedance increases by an order of magnitude over the same temperature range. The three-electrode impedance data of the A&T cells show that the increase in cell resistance comes mostly from the cathode electrolyte interface and very little either from the anode electrolyte interface or from the ohmic resistance of the cell. This suggests that the poor performance of the cells comes mainly from the high cathode-electrolyte interfacial impedance.