A power management method for electro-chemical batteries in low capacity state is provided, including: obtaining battery information based on device hardware, to know in advance the maximum allowable current and maximum allowable power when the battery power is low; by detecting the changes in the voltage versus current, updating BCC curve; using BCC curve as power budget to control the ON/OFF of device function thread; and determining whether the minimum battery capacity and the control restriction are reached, and when the minimum battery capacity and the control restriction are reached, turn off the battery through normal shutdown process; otherwise, return to the step of obtaining battery information.