More and more computers are mobile devices nowadays. The most important prerequisite for a portable computer is a chargeable battery which keeps the device powered.
Display of the charge state in the Dock: This is useful if you cannot or do not like to use the display in the menubar of Mac OS X, e.g. when you have a screen which is not very wide.
Display of internal battery information: In addition to the charge state, many other technical specifications, e.g. age, temperature, discharge current, number of charge cycles, or capacity can be retrieved. The states of each of the battery cells and the manufacturer of the cells can also be determined.