The terminal voltage of the supercapacitor can be expressed as:

Wherein:

• V_OC is the open-circuit voltage
• I is the current flowing through the cell
• ESR is the equivalent series resistance

When the system is in a charging or discharging state, the measured cell voltage does not completely represent its true energy storage state. If instantaneous voltage is directly used for balancing judgment, it may lead to incorrect balancing decisions. After the charge/discharge current is removed, the internal charge of the supercapacitor is redistributed, and the terminal voltage will slowly recover to a new stable value. This process is usually called the voltage relaxation effect (Voltage Relaxation). Therefore, making balancing judgments immediately after high-current working conditions end may overestimate or underestimate the actual voltage difference.