Looked all about and could not get an answer. Maybe someone here can help.
My W500, Win 7 got a bluescreen (crash) and when recovered the green battery icon in the task bar went also. I looked in the power manager V3.05 and it is ticked on the "options" page. Untick and re-tick no luck.
Uninstalled both the power manager and Thinkpad Power Management Drivers and re-installed, no luck. However, when re-installed I notice that the Power Manager was not available in the ThinkVantage folder in the "All Programs" folder. The only way to access it is in Control Panel under "Lenovo's Power controls"
Also the battery gadget has also gone (the one for the "sidebar").
Sounds like some file is missing or corrupted, or I have to re-install some driver.
Put the cursor over the "taskbar" area (or whatever Microsoft calls that strip across the bottom of the screen), right-click on it, choose "Toolbars", then see if your battery gauge appears as an unchecked choice in the list of available toolbars. If it does, check it.
W520 (4270 CTO), which replaced a W500 (4062-27U), which replaced a T42P, which replaced an A21P...