XBattery is a battery monitoring tool for Mac OS X computers. The application is incredibly lightweight, and very simple. It consists of a main window that shows the current battery level. in a graph from 100% to 0% on the Y axis and the time on the X axis. If your computer is connected to AC, this graph will be really useless. From the bar menus, you will be able to open some other windows with information and graphs. There is a battery voltage graph, a battery current amperage graph, a battery capacity graph and a window with information about your battery. Out of all the windows, the one I found to be the most useful is the Info window. It shows whether there is a battery installed, if it is charging or not, the battery charge in percentage, the maximum capacity, current capacity and charge and the voltage. The most useful piece of information for me is the cycles that my battery has on it. The more cycles, the less of a charge the battery will hold.
All in all, this is a tiny utility that can show some information about your battery. I don't think the $15 price tag is justified when you can get all this information from the system profiler app.