  A voltage-based method is proposed to correct battery pack state of charge
(SOC) estimation at the charge-end. Two main characteristics make the
charge-end time span a good opportunity to correct SOC estimation: first, it is
easy to detect when the battery is at the last stage of charging because the
charging profile is known to the BMS designer and also during the charge-end
time span the amount of current is low, and the terminal voltage of the battery
cells are high; second, as the battery reaches the charge-end stage, we know
that the true SOC is approaching to 100%. This paper presents a method to
utilize these important features to correct the SOC estimation error. Using a
voltage threshold method, the algorithm detects when the battery is close to
the charge-end to activate the charge-end SOC correction strategy. Once
activated, the strategy corrects the SOC using the maximum cell voltage to
guarantee that SOC is 100% when charging is complete. The amount of correction
is a function of maximum cell voltage and the charge current C-rate.
