A battery monitoring system (BMS), which utilizes a minimum amount of input data (time, voltage, current, temperature and conductance, for example) to periodically determine a vehicle battery status or condition is provided. The BMS combines electronic hardware and software to give logical and critical data to assess and control a battery-based electrical system. The BMS can include processing circuitry (a microprocessor, for example), which is coupled to a voltage sensor, a current sensor, a temperature sensor, etc., that provide the necessary input data for the microprocessor, which executes program code, to determine the vehicle battery status or condition. A method of monitoring a battery in an operating vehicle is also provided.