Electrochemical impedance spectroscopy offers an alternative method of performing nondestructive characterisation of electrodes and batteries in stationary power stations compared to the more conventional discharge tests. A model for porous electrodes is used to analyse impedance data in such a way that physical parameters can be evaluated. It is also suggested that these parameters can be used as a way of determining the state of health of a battery during float charging. A method for the calculation of the steady-state current of porous electrodes is also presented, based on the impedance model. The combined d.c. and a.c. analysis confirm more concisely the validity of the theoretical assumptions used to explain the experimental data.