The storage of nickel/metal-hydride (Ni-MH) battery with co-precipitated cobalt hydroxide and post-added cobalt compound as the additives for pasted Ni(OH)(2) electrode is studied in this paper by using galvanostatic charge-discharge, cyclic voltammetry and X-ray diffraction (XRD). lt is shown that (I) capacity loss occurs only on the battery with post-added cobalt compound during the storage; (II) CoOOH derived from co-precipitated cobalt hydroxide has a better stability than the one from post-added cobalt compound and an irreversible reduction of the latter is observed; and (III) an inactive Co + 3O(OH) is obtained from Ni(OH)(2) electrode with post-added cobalt compound after the storage and should be responsible for the property deterioration of Ni-MH battery. Thus, it is important to increase the stability of CoOOH derived from post-added cobalt compound when Ni-MH battery suffers a long-term storage. (c) 2006 Elsevier B.V. All rights reserved.