Screen is very dim when using battery power

I have Inspiron 9100 notebook. The screen is very dim using battery power. Is this a backlight problem and if so is backlight built into the screen or is there a bulb to replace?

If the notebook screen is very dim only when it runs on the battery power, most likely this is not a hardware related issue. Check your notebook power settings in the control panel. It’s possible that your LCD screen brightness is set to minimum when the notebook runs on the battery power. Usually, you can adjust settings in the control panel, in the power management utility. You can change screen brightness for AC and battery modes separately. On some laptops you can change screen brightness settings in the BIOS setup menu.

Here’s an example of adjusting the LCD screen brightness on a Toshiba laptop. You can do it through Toshiba Power Saver utility in the control panel.
As you see, when the notebook runs on the battery power, you can you can adjust the screen brightness at a few different levels.
When the battery power goes down, the LCD screen gets darker.

Screen brightness

Different notebooks use different power management utilities, but the idea is the same.