In 1749, Benjamin Franklin coined the word battery for a series of capacitors connected to store energy. Capacitors store electric potential energy that can be released over a short time. This property means capacitors have a wide range of applications.

Capacitor-discharge ignition is a type of ignition system commonly found in small engines where the energy released from a capacitor ignites an induction coil that, in turn, fires the spark plug.

To calculate the energy stored in a capacitor of a typical CDI system, at least two of the following parameters should be known:

1. The voltage applied across the capacitor
2. The charge stored in the capacitor
3. The capacitance of the capacitor

Since these three parameters are related by the equation given below, the unknown parameter can be calculated if any two parameters are known:

For any given case, the potential energy stored can be calculated using the values of capacitance, voltage, and charge: