Supercapacitors have a very wide range of uses. Combined with high-energy-density substances such as fuel cells, supercapacitors provide rapid energy release to meet high power demands, allowing fuel cells to be used only as an energy source. At present, the energy density of supercapacitors can be as high as 20kW/kg, and has begun to seize the market between traditional capacitors and batteries.

In applications that require high reliability but low energy requirements, supercapacitors can be used to replace traditional batteries, or supercapacitors can be combined with batteries. Supercapacitor modules are used in applications that require high energy, while Smaller, more economical batteries can be used.

Any supercapacitor will discharge through the internal parallel resistance when it is energized. This discharge current is called leakage current, which affects the self-discharge of the supercapacitor unit. Similar to some secondary battery technologies, the voltage of supercapacitors also needs to be balanced when used in series, because farad capacitors have leakage current, and the size of the internal parallel resistance determines the voltage distribution on the supercapacitor cells in series. When the voltage of the supercapacitor is stabilized, the voltage on each unit will change with the leakage current, not with the capacitance value.

The discharge of the supercapacitor cell reduces the voltage, which in turn affects the voltage of other cells in series with it, assuming that these cells in series are powered by the same constant voltage.

In order to compensate the leakage current change, the supercapacitor manufacturers often use a method to connect a resistor in parallel next to each unit to control the leakage current of the entire unit. This method effectively reduces the variation of the corresponding parallel resistance between the cells.