Dell XPS (9350) - Power button works only when plug in

Hello,

I just recently changed my laptop battery for XPS 9350 model. The process was painless but I encountered an odd issue after the change:

If I shutdown my laptop and leave it for a few hours the power button fails to turn it back on again. However, if I plug in power adapter briefly (until i see the led light up) then unplug it; the power button works and I am able to turn it back on (even with the adapter unplugged).

Power button also works if I shut it down and in immediately power it back up again. 

I am almost 99% sure it is not the battery and would like to get some input on this strange behaviour

Additional information:
- the battery was at 100%

- the battery is from dell

- and I can run off battery with no issues if it is powered on and unplugged

- I have also run battery diagnostics from BIOS and Support Assist Application (no issues)

Thanks,

Ken