This paper presents an online impedance measurement method for energy storage batteries, which achieves a broadband impedance measurement by segmenting the measurement through the DC-DC converter within the battery energy storage systems. This method divides the impedance into two parts according to the switching frequency characteristics and harmonic characteristics of DC-DC converter. For the low-frequency range, impedance is measured by sinusoidal sweep using an alternating reference voltage. In the high-frequency range, impedance measurement is realized by adjusting the switching frequency of the DC-DC converter based on its triangular waveform characteristics, covering high and ultra-high frequencies. Discrete Fourier transform is introduced to process the collected current and voltage data. By extracting the frequency domain information under the response harmonics, the battery impedance is calculated. A battery energy storage test platform is constructed to measure the battery impedance from 1000 Hz to 9000 Hz, thereby validating the effectiveness of the proposed method.