Theoretical cell model is applied for evaluation of valve-regulated lead–acid batteries under discharge, recharge and overcharge conditions. The previously presented models are improved by introducing a new formula for electrode morphology, applying charging factor to state-of-charge, electrode porosity and acid concentration as well as considering the recombination of oxygen as mass-transport limited evolution process. Also, a new model is proposed for the ohmic resistance of a battery. The modified cell model is calibrated using experimental data. Results show that high prediction accuracy can be obtained for the full discharge–recharge cycle including deep discharge and overcharge. The modified cell model is applied for evaluation of the gas formation processes using externally measured current, voltage and temperature of a battery.