Abstract: In view of problem of leakage current in voltage measuring method for single battery in series batteries based on operational amplifier and MOSFET, an improved voltage measuring method was proposed. Voltage follower is added at two ends of each battery to reduce leakage current effectively; photoelectric relay is added as power switch of operational amplifier to make voltage measuring circuit not consume current under status of power off; zener diode is added to prevent breakdown of MOSFET. The test result validates effectiveness of the improved method.