Nickel hydroxide electrodes have been studied by ac impedance spectroscopy at rest potential and during charge or discharge. A transmission line model is proposed based on behaviour similarities with electrochemical intercalation into graphite. Considering here that protons and electrons react inside the solid, partial electronic and protonic conductivities of the two beta-type phases Ni(OH)(2) and NiOOH in equilibrium are taken into account. Even if 1-D and so basically limited to a homogeneous deposit of constant thickness, this model approximates reasonably experimental observations.