Decide when the screen turns itself off

A screen that goes dark after two minutes while you are still reading it is a setting, not a fault. The timers live in System Settings → Lock Screen, and there are two of them: Turn display off on battery when inactive and Turn display off on power adapter when inactive.

Keep the battery one short — two or five minutes. The display is the single largest drain on a laptop, and the minutes you claw back there are worth more than any other power tweak.

Set the plugged-in one long enough that reading a long page never blanks it. Twenty or thirty minutes is usually right.

Underneath sits Require password after screen saver begins or display is turned off. A short delay there is the sensible compromise: the screen goes dark quickly to save power, but you get a grace period before it asks for the password when you sit back down.