I'm assuming windows 10 is on the computer...….

I suspect the battery is failing or has failed, most likely needs battery replacement. The AC adapter being detected or saying it's type in BIOS, indicate adapter is working normally, also a good sign DC Jack isn't loose or damage. If the computer is connected to an wall outlet, the battery light operates as follows

Alternately blinking amber light and white light - An unauthenticated or unsupported non-Dell AC adapter is attached to your laptop. 

Alternately blinking amber light with steady white light - Temporary battery failure with AC adapter present

Constantly blinking amber light - Fatal battery failure with AC adapter present.

Light off - Battery in full charge mode with AC adapter present.

White light on - Battery in charge mode with AC adapter present.

Battery Status Lights

https://www.dell.com/support/manuals/us/en/04/latitude-e5440-laptop/delllatitudee5440_om-v2/battery-status-lights?guid=guid-b7187258-116a-4cf7-8b00-704729aa7883&lang=en-us

You mentioned  Battery Health is Okay in BIOS. What does it really say, Battery Is Performing Normally or Battery is fair ?

Excellent — Battery is operating at maximum capacity.

Good — Battery can charge normally; however, you may notice reduced operating time because long-term battery life is decreasing.

Fair — Battery can charge normally; however, it is near the end of its usable life. It is recommended that you purchase a new battery soon.

Poor — Battery no longer provides sufficient power. It is recommended that you replace this battery.

Battery no longer operates, or battery status cannot be determined. It is recommended that you replace the battery.

Yes, I use windows 10.

There's no blink at all, the battery light is white on for few seconds (2-5 seconds) and then switch off until I plug/unplug my adapter.

The battery health was Good in BIOS. 

I forgot to try another wall outlet 

@LSUFAN51 

 " The battery health was Good in BIOS "

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The battery appears to be in great health. What happen when you tried another wall outlet? The battery start working again? Thanks for the update.

Going through the exact same problem but on a 7450. Did you ever figure this out?

EDIT: I'm unsure if the BIOS options would be the same but figured I'd post just in case it helps any. There's an option in BIOS on the E7450  - "Wake on AC Power", that helped me out a bunch. Now all I have to do to turn on the laptop is plug in the charger. From there I can unplug if I want to go portable. I figure the power button or DC is my culprit here since I can't power on the laptop using the power button w/ or w/o AC being connected. Just get a half second on/off white battery indicator light when I plug the charger in and w/ Wake on AC Power that's enough to get it going.