Inspiron 14 7472, concern not turning ON

My concern is the laptop is not turning ON.

I shutdown the laptop and let it rest for about three hours, and when i'm going to use it again it's not turning ON.  even I plug in the AC adapter and press the power button still not turning ON.

I tried to press and hold the power button for about 1min to discharge, still no hope.

here is the video for reference.

See video here.

Now I tried to remove the bottom cover of laptop and remove the battery,  then pressed the power button for 1min to discharge. (without battery)

After I do the discharging thing I re-attached the battery again and tried to turn on the laptop, still not turning ON (FYI: battery is full after  I shutdown the Laptop)

now I tried to connect the AC adapter to the laptop, and the laptop keyboard led turns on, power button led indicator turns ON, and led light indicator near touchpad turns ON. 

I notice that the LED light indicator near touchpad blinking 3times fast and 2 blinks slow. then everything will turn off.. then it will turn on again all the LED, then turn off.. and then turn ON again. and now it has a display... it display the SupportAssist and it has a message ( Invalid configuration information, Please run setup program - time and day not set, please run setup program) BIOS has been reset? so then i just press continue and boot from the operating system and it will continue. then shutdown the laptop. and when I press the power button again it will not turning ON even the AC adapter is connected. Even I unplug and plug in the AC adapter still not turning ON. (FYI: battery still attached here.)

here is the video for reference

See video here.

Now I tried to completely remove the battery and do the discharge thing again, now I run directly the laptop from AC Adapter without the battery. and same scenario happens the LED lights thing.. and so on etc.... after that it will proceed again to operating system and then i tried to shutdown again the laptop and tried to press the power button again still it will not turning ON. this time it will turn on if you unplug and plugin the AC adapter. it will repeat the same scenario of LED light thing and support assist will display again BIOS has been reset again? etc... and proceed again to the OS.

(My Question here is this normal thing? if you run the laptop directly from AC adapter..without the battery?)

Now I conduct a diagnostic (Support Assist) 

after the diagnostic the results says (The Battery Is Reaching The End Of It's Usable Life).

before I will buy a battery my question is it just the battery the problem?

further questions:

1: Will the laptops turns ON even the battery is defective and still attached, if you just plug in the AC adapter? or do we really need to remove the battery and plug the AC adapter before it turns ON.