Most, if not all, spacecraft require some form of energy storage medium. The requirements for the type and configuration of energy storage are generally dictated by four main factors:

1. The environment in which the spacecraft is operating (i.e. orbital parameters dictating eclipse period and frequency, thermal considerations).
2. The mission life expectancy.
3. The operations profile and power requirements of the mission itself.
4. Mass and volume budget constraints.

The most commonly used form of energy storage are Secondary Batteries. It should be remembered, however, that there are alternatives to this stalwart method of storing power. These alternatives include Primary Batteries, Fuel Cells, Mechanical Energy Storage and Super Capacitors.

Another reason not mentioned above which must also be considered is the finance budget and schedule considerations of the mission. Secondary batteries mostly provide the most cost effective solution due to the fact that the technology is widely available, but also because most power system architectures and electronics are designed to interface to this means of energy storage. If the mission requirements lend themselves to a less standard means of energy storage this can have serious impacts to the rest of the spacecraft subsystems.