Why can I only change my screen brightness when my laptop is charging?

Just did a recent update on Windows 10. I can't change my screen brightness by pressing the increase/ decrease brightness button on my keyboard. If I do press the brightness button, I am still able to click and drag to change the brightness. When my laptop is plugged in I do not have this issue.

Can someone help me here? I am really frustrated.

spunk said:

This is one of the power options. Go to Start/Search and type power options. You should have two settings, one for battery only and one for being plugged in. Running at full brightness will drain the battery faster.

I used to be able to change the brightness by pressing the keys before. That's what I am trying to fix.

I've also experienced that on a couple of Notebooks [different brands] and it seems Win10 is over-riding the ability of the Fn key in favor of the setting in Power Options [Control Panel]. I haven't actually found proof of that except for what I've seen.