Patent ID: 8872518

Claim:
A method of determining a state-of-charge of a battery within a system powered at least in part by the battery comprising: collecting a plurality of voltage measurements from the battery during operation of the system; deriving a time-constant of relaxation and an open-circuit voltage corresponding to the battery from the voltage measurements and a mathematical model of the battery that relates the voltage measurements to the open-circuit voltage and the time-constant of relaxation; and, estimating the state-of-charge of the battery based, at least in part, on the open-circuit voltage; wherein the mathematical model comprises a closed mathematical expression that includes the open-circuit voltage and the time-constant of relaxation; and, wherein the closed mathematical expression is of the form: V(t)=OCV−αe t/τ , wherein V(t) is one of the voltage measurements at a given point in time, OCV is the open-circuit voltage, α is an overpotential, and τ is the time-constant of relaxation.