If you are a Laptop user than the Battery bar is the must have utility for you. Apart from showing the estimated time remaining and percentage available it also shows the charge/discharge rate. But One thing I really liked is the Battery Wear. This really helps you to know how much your battery has deteriorated. You can see you battery wear status and be alerted at advance and start using your laptop battery wisely.
The Battery Bar comes with the two version free and the pro. For general purpose the free version should be enough to give the necessary details. You can check the software from this link http://osirisdevelopment.com/BatteryBar/index.html
If you are using the windows 7 or vista then you may get the message ?Consider replacing your battery?. This is usually due to the maximum wear percentage of your battery. If your windows is not showing the time remaining when you are on battery backup then this tool is the must have. This tool even shows the time remaining when the windows stop showing the available time remaining. So have it installed on your laptop or notebooks or netbook before you know its too late.
You can visit the following link to know more about battery. This site gives you clear idea to handle lithium ion battery properly.
Have a long life battery.