The process and mechanism of zinc electrode shape change is investigated with the radiotracer technique. It is shownthat during repeated cycling of the nickel oxide/zinc battery zinc material is transported over the zinc electrode via the battery electrolyte. During charge as well as during discharge zinc material is transported over the electrode. The direction ofthe zinc material transport during charge is opposite its direction during discharge. The amount of zinc material displacedover the electrode during charge is smaller than during discharge, so that after one charge-discharge cycle the net zinc material transport is observed in the direction as found during discharge. A new model for shape change is presented: thedensity gradient model. The model is based on the occurrence of an electrolyte flow during repeated charge-discharge cycling of the zinc secondary battery, which transports zinc material over the electrode. During battery cycling this electrolyte flow arises as a result of density gradients in the solution layer adjacent to the zinc electrode and of volume variationsof the battery electrolyte.