A method of monitoring a battery includes measuring an open circuit voltage (V.sub.oc) on the battery to determine a measured state of charge (SOC.sub.m) after at least one use, obtaining a calculated state of charge (SOC.sub.c) based on a state of charge prior to the at least one use and a discharge of the battery during the at least one use, and determining a state of the battery based at least in part on a difference between the calculated state of charge and the measured state of charge.