Now I remember I once had a similar problem with the Battery Monitor control panel. A reading that was way too high.
I eventually solved it. I tried the simple troubleshooting tips first, because the simple things are often where Windows .
One tip not mentioned yet is to remove the battery. Run the laptop on AC for a session or two. Create some change in the battery monitor circuitry, or the monitor software data. Any change might do the trick.
Install the battery again. See if things behave better.