I love the feature when Windows sets different backlight level depending whether I am plugged in or on battery. I really fits how I use my laptop. But then one day that feature seemingly disappeared. Cause seemed to be a Windows Update and to fix it I would essentially need to restore my old driver.
Well, either that or this small utility. Once installed, it will run a service in the background tracking your power source and backlight level. Whatever level you last set on battery will be used whenever you unplug and whatever you set while plugged in will be used when your AC adapter is connected. Essentially, the same behavior as what once came by default.
While this will never be a full application as I doubt there will ever be enough interested people, download is available at GitHub.
PS: For Linux version check Backlight Tracer.