The possibility of replacing, with electric drive systems, at least some of the internal-combustion engines currently employed in road vehicles is being actively pursued by all the world＇s major automobile manufacturing companies. Minimum on-road emissions would be achieved by the adoption of pure electric vehicles, but the somewhat limited range available between charges of the batteries has led to a serious evaluation of hybrid electric vehicles as an acceptable compromise. In hybrids, a small internal-combustion engine, operated at high efficiency, will consume less fuel and produce less emissions than would a regular internal-combustion engine, and will allow considerable range extension over the pure electric vehicle. Eventually, an electric system which employs a fuel cell may become affordable. It is likely that all three systems - the pure electric, the hybrid electric, and the fuel cell system - will require battery support, particularly to provide boost power for acceleration and hill climbing. Although more expensive battery systems are being vigorously developed in pursuit of greater range per charge, the benchmark against which these systems are compared remains the valve-regulated lead-acid (VRLA) battery.