Equivalent circuit components of nickel–metal hydride battery at different states of charge

Equations that describe the voltage variations with time of rechargeable batteries during charging and discharging were used to determine the component values of the equivalent circuit of nickel–metal hydride batteries under different states of charge (SOC). The equivalent circuit of the battery was described as an ideal voltage source in series with a resistor and the parallel combination of a resistor and a capacitor. The battery model used different values of resistance and capacitance, in the parallel combination, during the different phases of the discharge–rest–charge–rest sequence. The results show that the resistances in the equivalent circuit are approximately constant with variations in the SOC. For the discharge and charge phases the capacitor value increased and decreased, respectively, as the SOC decreased. The value of the capacitor in the parallel RC circuit is an indicator of the battery SOC.

► The equivalent circuit of nickel–metal hydride batteries is presented.
► Parameters are given for different states of charge.
► Resistance is constant at different states of charge.
► Capacitance varies with state of charge.
► The capacitor value is an indicator of state of charge.