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.