Battery icon not updating windows 7
If the issue is persistent, it may be worth downloading newer drivers directly from your manufacturer.
Below is a solution for resetting the Windows 7 default ACPI battery drivers.
One can quickly switch between power plans by clicking on the battery icon.
While this battery icon always appears in the system tray area of the taskbar, sometimes you might find that the icon is missing from the taskbar.
The battery icon on the panel only changes when I restart or log-out then log back in.
For example, my battery is low at 15%, however, the icon indicates its at 79%, which was the percentage when I first booted into the OS.
Right-clicking on the batter icon provides quick access to Power Options, Windows Mobility Center, and Adjust screen brightness.
It may be worth cleaning the cooling ducts and CPU/GPU heatsinks with compressed air/vacuum.