A method for checking and modulating battery capacity and power based on charging/discharging characteristics is provided. In terms of discharge, a relationship between an open circuit voltage and an output electric capacity of a battery is measured to obtain a first characteristic curve. A relationship between a voltage and the output electric capacity of a battery at a predetermined maximum charge/discharge current rate is measured to obtain a second characteristic curve. A characteristic boundary line passing the first and the second characteristic points respectively selected from the first and the second characteristic curves is established. A voltage value corresponding to the first characteristic point is higher than a voltage value corresponding to the second characteristic point. The first and the second characteristic curves, and the characteristic boundary line define an operation range. The battery is charged/discharged within the operation range.