The dynamic behaviour of batteries can be predicted using theoretical cell model for basic processes. In this paper, this model is calibrated for two types of valve regulated lead acid (VRLA) batteries, and is applied for viewing unobservable processes in battery by observable processes. It is shown that unobservable parameters like overpotential, reaction rate, porosity, acid concentration, and other parameters of electrode can be evaluated by total current, terminal voltage and temperature of surrounding atmosphere of battery. The calibrated model is applied to distinguish between outwardly equal batteries with different backup time and cut-off time. It is shown that difference in morphology of electrodes, thickness of electrodes and quantity of electrolyte in separator are the main distinguishing parameters between batteries. These parameters can be tested online by current–voltage measurements using fast calculation method proposed in this paper.