The backup characteristics of lithium-ion batteries were investigated using commercial prismatic lithium-ion cells with a LiCoO2/graphite cell system. An accelerated method of estimating the lifetime of lithium-ion batteries was developed. It was found that higher temperatures and voltages accelerate the degradation of the cells: a 15 degreesC increase in temperature cuts the cell life in half, and about 0.1 V increase in charging voltage also cut the cell life in half. (C) 2003 Elsevier Science B.V. All rights reserved.