The built-in battery manager in Windows can be deceptive in its reports of how much time is left before the battery dies.
BatteryCare is a software created to optimize the usage and performance of the modern laptop's battery. It monitors the battery's discharge cycles and helps increasing it's autonomy and improving its lifetime. The program sits in the system tray like the Windows battery monitor, but gives much more information when your mouse hovers over it.
It tells your battery’s percentage charged, the temperature of your CPU and hard drive, and your current power setting.
If you click the icon in the System Tray, you can change your Power Saver setting with just one click.
Right-clicking the BatteryCare icon in the System Tray brings up another menu that allows you to change your power plan, adjust settings, or show the program’s main information screen.
Click Show at the top of the menu to see more information about your battery, or double click the icon in the System Tray.The first screen that appear is basic information, further describing your battery’s current health. This is where you can find out how much battery life you have before finding a place to plug in.
Click Detailed Information towards the top right of the window to bring up a menu with information about your battery’s designed capacity, current capacity and wear level. This can help you predict if it is time to buy a new battery.
Clicking the Settings link at the top right of this window brings up configuration options for getting the most of BatteryCare and your battery.
Most of the general settings are self explanatory, like starting the program when Windows starts, but there are added settings to disable the Aero theme in Vista (it worked in Windows 7 too) and to pause services. This can extend your battery life at least a few extra minutes.
You can also change the temperature to be displayed in Fahrenheit instead of Celsius
BatteryCare is superior to the built-in Windows battery monitoring functions. It gives more information about the battery and over time, its statistical calculations about discharge cycles and how much time you have left on the current battery charge improve. If you use your laptop’s battery on a daily basis, this program is worth the download.
Battery Care Download Link: http://batterycare.net/en/download.html
See also Proper laptop battery usage guide