Battery Drains unreasonably fast when in use and power off

[LQL]

Hi, I've recently bought my laptop and it's only 3 weeks old. I've used it for less than 10 times. I've notice that my power battery drains rather unreasonably fast when in use and when it's switched off (power off/ shut down).

My Operating system is Windows 10 20H2 (OS19042.746)

When using, I only mainly do work, the normal website searches and with youtube music as a back ground. 

I've kept a note on the power drain within my usage timing and its as follows (is the amount of battery % drain within normal range?, see within almost 2 hours my battery is somewhat left with half)

2pm - 100%
2:15pm - 94%
2:20pm - 91%
3pm - 91%
3:23pm - 74%
4pm - 63%

My settings is on battery saver and the brightness is reasonable.. (~30 to 40)

When it's shut down/ power off

I have my laptop charged to 100%. and didn't use it for about 6 days and when I tried to power on.. it was dead... so I believe the battery was 0% which was crazy.. cos I didn't expect it to drain till its dead.. 

I do expect some draining but not till 0% !!!

(I am 100% sure it was shut down properly and correctly.. no way was it in hibernation or sleep mode!)

I know how Li-ion battery works and understands that it'll drain... but my is ridiculously fast with minimal usage...

I've also already read up on how to save battery/ prevent battery draining, I've done the following:

1. disable usb when power is off

2. check and update the BIOS, chipset and graphics driver

3. update all windows updates

4. run test on battery and hardware

5. change of power plan (can't change as its only balance in this Windows 10)

NONE OF THE SOLUTION ABOVE WORKS! not only that.. my laptop flickers at random times as well...

Please help or do I need to exchange for a new one?!?!?! This is really upsetting and disappointing...