# What's the difference between energy and power?

The electric potential difference, a difference in charge, between two points is what we call voltage. Using the analogy of a water tower, voltage can be thought of as the difference in pressure between the level of water in the tower and the end of a hose attached to the tower. The higher the water level the larger the difference in pressure.

If we open the end of the hose we permit the pressure to push a flow of water. This is a conversion of potential energy into kinetic energy. The electrical equivalent of this concept would be if we were to complete a circuit permitting the potential difference or voltage to be converted into electrical energy. This energy pushes a flow of charge called current. Energy is measured in joules.

Power is the rate at which energy is used. The number of joules used per second is known as the watt, the standard unit of measure for power. As an example of how energy and power relate to one another consider the Batt Pack Energy. The Batt Pack Energy has what can be considered a reservoir of energy of 2.5kWh (kilowatt hours). If you have an application that runs at 1.25kW you simply divide the kilowatt hours by the kilowatts to determine that you can run your application for 2 hours continuously.

To use another analogy, your energy in kilowatt hours can be considered your fuel tank and your power in watts is the rate at which you burn fuel. 