Lead- acid battery is the most economic and reliable energy storage device. It has been widely used in uninterruptible power supply (UPS) systems and back-up power systems. How to prevent the battery from the failure of supplying power without alarm is an important issue. The real-time display information of state-of-health and residual capacity of battery can improve the reliability of battery. In this paper, a battery monitor system to supply the real-time information of state-of-health and residual capacity of battery set is developed to improve the reliability of battery set.