This beats the hell out of the built in battery guage. For free you can’t knock it.
SlimBatteryMonitor is a replacement power gauge for Apple’s Mac OS X that tracks both laptop batteries and many UPS batteries. Multiple-battery systems (e.g. older powerbooks) are supported as well. A graphical icon shows the power remaining, and can be accompanied by a text description (battery charge in percent, or time remaining). Colours can indicate whether the system is fully charged, charging or on battery.
three different text displays
show percent full or time remaining
five different shape options
5 different shape options
much smaller than mac os x gage
much smaller than Apple’s gauge!
Best of all, you can choose different display options for each battery state (fully charged, charging or on battery). You may wish to see the time remaining while on battery, for example, but show only the icon during charging, and hide SlimBatteryMonitor entirely when batteries are fully charged.