NOVELTY - The method (78) involves predicting (86) terminal voltage of battery module in vehicle using battery control module. The gassing current that quantifies terminal current not used to charge battery module, is determined. The predicted terminal voltage is calculated based on measurement model and gassing current. The terminal voltage of battery module is measured (88) using a sensor coupled to battery control module. The corrected state of battery module is determined (94) using battery control module by minimizing error between predicted and measured terminal voltages.    USE - Method for recursively determining state of lead-acid battery system in vehicle (claimed).    ADVANTAGE - The corrected state of battery module is determined using battery control module by minimizing error between predicted and measured terminal voltages. Thus, the accurate determination of the state of a battery enables the vehicle control module and/or the battery control module to assert more control over operation of the battery module. The gassing reaction is quantified through a gassing current model, which enables the amount of current actually used to charge the battery system to be determined with the improved accuracy of the state of charge. Thus, the stability of vehicle operation is improved because there will be less error in the determined state of charge. Since the state of charge is determined with more certainty, the fuel efficiency is increased and the emissions are decreased because the internal combustion engine is disabled for longer periods of time without potentially jeopardizing vehicle operation stability.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a vehicle; and    (2) a tangible non-transitory computer-readable medium storing program for.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart illustrating the method for recursively determining state of lead-acid battery system.    Method for recursively determining state of lead-acid battery system (78)    Step for predicting terminal voltage of battery module in vehicle (86)    Step for measuring terminal voltage of battery module (88)    Step for minimizing mean square of error (92)    Step for determining corrected state of battery module (94)