This research proposes a smart battery management system applied to Li-Battery. The system not only can monitor the batteries for all kinds of parameters but also modify them by users. Besides, in estimating the residual capacity of Li-ion batteries, an automatic measurement platform is set up in order to record the data of Li-battery in different kinds of charge-discharge condition and to analysis the characteristics. In monitoring used battery capacity, Modified-Coulomb-Measuring method is proposed and it can accurately estimate the residual capacity according to the effect of output current and environment temperature. In addition to estimate the residual capacity accurately, Smart Battery System can record the information of Li-batteries over a long period of time, and the log files can be used for further battery characteristics analysis.