The identification precision of model parameters would be affected by the amplitude of signal by using step-change current to identify battery parameters. In this paper, error analysis of this parameter identification method applied in battery dynamic models is carried out to address this issue. And a method to determine the amplitude of step-change current is proposed. Battery nonlinear characteristics and measure error caused by the detection devices are considered to identify the function between the relative error of parameters and the amplitude of step-change current. The amplitude determination procedure is given in this paper. Analysis and experiments verify the feasibility of the proposed method.