How to Monitor Your Laptop’s Battery in Windows Vista
You can keep an eye on how much battery life your laptop’s battery has by viewing the tiny battery icon on the system tray. The icon graphically shows how much power is left; the icon's color "drains" out as you use the laptop. Often, that display is too tiny, so what you can do is point the mouse at the icon to see a pop-up bubble explain how much juice you have left, similar to what's shown here.
Displaying the battery icon in Windows Vista
To ensure that the battery icon shows up in the notification area, heed these steps:
Choose Control Panel from the Start menu.
Click the Taskbar and Start Menu icon in the Control Panel window.
Click the Notification Area tab.
Put a check mark by the Power item.
You can also monitor battery usage from the Control Panel's Windows Mobility Center in Windows Vista.