In this paper, a novel fast battery impedance online identification method based on double side band small signal injection through controlling of the battery-connected inverter is proposed. The principle of double side band small signal injection and impedance identification has been discussed. This method takes short time and shows high accuracy while hardly affects the normal operation of the system. It is economical since there is no need to add extra signal injection equipment but using the existing battery-connected inverter in application. In view of the widely-used battery-inverter topology in electrified transportation field, this method has potential to popularize in future. Comparing with the constant-amplitude AC signal injection, the double side band small signal injection method can be with more frequency points in identification with the same period.