Originally posted by: ahurtt
My laptop, with WinXP Pro, automatically pops up a little battery icon on the system tray when I am running on battery power. Mousing over the icon tells what percentage of the battery power is left and how much longer the battery is expected to last. You can access this feature by going into Control Panel -> Power Options and going to the Power Meter tab. Put a check in the checkbox labeled "Show details for each battery." You didn't say what OS you are using but I'll assume it's some Windows version.