The battery management system (BMS) is substantial in diagnosing and controlling the battery modules of emerging electric vehicles (EVs). This paper presents a cost-effective stimulus generator for characterizing the communication channels between the BMS host controller and the battery cells. The characterization data are useful to enhance the reliability of the communication. The proposed stimulus generator only consists of a digital oscillator, a reconfigurable digital ∑-Δ modulator, and an output driver. The all-digital design saves the power and the hardware cost. The digital oscillator provides digital sine waves with well-controlled frequency and amplitude. The proposed reconfigurable digital ∑-Δ modulator allows generating pulse-density-modulated (PDM) bit-streams of particular frequencies that cover the whole band of interest. Hence, the test accuracy is no less than that of conventional sinusoidal waves. Simulation results show that the generated stimuli have very high narrow-band SNRs that is essential to test the frequency responses of the channels.