The recently commercialized sealed nickel metal hydride (NiMH) battery is well suited to applications where high energy density, high rate charge/discharge and good service life are required such as in wireless mobile communication applications. The objective of this study is to obtain insight on the cyclic performance of duty operation in practice and primary failure mechanisms of the NIMH battery with high energy density st the end of cycle life in conventional analog and novel digital operations by using the electrochemical impedance spectroscopy (EIS) technique. Simulation of digital operation demonstrates a considerably shorter cycle life of the battery than that in analog operation. The mechanisms of the earlier performance loss in digital applications and wear out of the battery in conventional applications are studied by using the EIS method. This study gives the effects of internal impedance and other kinetic characteristics of the NiMH battery on the overall performance. Results indicate that stable low internal impedance over the prescribed service life shall be mainly taken into consideration;in the selection of the NIMH battery with high energy density particularly for digital applications and the cyclic performance of the battery may be improved to the same level as that in conventional analog applications.