Mobile systems with lithium-ion batteries have become very popular. Higher performance, longer battery life, and safer operation are required for those systems. We have developed a method of the thermal management system for lithium-ion batteries for mobile systems. An evaluation system has been built with micro-processor with analog interface, and FPGA. It provides a charge and discharge speed control to manage the temperature condition. An application to variable speed charger shows that battery can be charged in short time with less temperature rise.