Patent ID: 7902829

Claim:
A battery management system comprising a plurality of battery cells, the system comprising: a voltage and current sensor for the battery that generates voltage and current signals concerning the battery; and a main controller that receives the voltage and current signals from the sensor and is configured to: (a) measure a key-on open circuit voltage (OCV) using the battery voltage signal, (b) determine whether the key-on OCV belongs to a first OCV region or a second OCV region, and (c) estimate an initial state of charge (SOC) of the battery using a linear equation when the key-on OCV belongs to the first OCV region; wherein the main controller is further configured to calculate the key-off time period, the key-off time period being an amount of time that the battery has been in a key-off state from a key-off time point to a time point at which the present key-on state begins, and to compare the key-off time with a reference time; and wherein when the key-off time is longer than the reference time the main controller determines whether the key-on OCV belongs to the first OCV region.