Apparatus for recharging a battery, comprising a compartment which holds the battery so that its electrical terminals are in contact with a pair of electrodes. The electrodes are connectable to the poles of a controllable source of electrical energy. In the compartment a ferromagnetic body is positioned so as to be subjected to mechanical stress in response to mechanical deformation of the battery. An electrical device monitors the magnetic permeability mu of the ferromagnetic body by measuring the self-inductance of a coil surrounding at least a portion of the ferromagnetic body. The mu of the ferromagnetic body changes by magnetostrictive effects arising from mechanical stress of the ferromagnetic body in response to mechanical deformation of the battery (5) during charging. Expansion of the battery can be used as an indicator that charging has been completed, and that the battery should be disconnected from the source of electrical energy.
