Latitude 3440's screen backlight stay on even after shutdown

My Latitude 3440 recently have this problem. After shutdown, meaning complete shutdown (no fan were running, no heat, no power light, nothing is running), but the screen's backlight (specifically the bottom right one) was on and shining. I didn't notice it until recently, so I don't know exactly the cause of the problem.

If I touch the battery and move it a little, the light starts flickering (not on and off, but more like brighter and dimmer each time). If I completely remove the battery, the light starts fading then turned off. If I plug in the cord (even without battery), it will come back up. I don't notice any difference in brightness between with the cord and with battery.

The laptop's display is normal when running.

I suspect that this is a hardware problem that I need to go maintenance, correct? Or is this a bios problem?

Any advice would be great. Thank you guys in advance.