Why is my brand new Apple Watch Series 5 (2019) not turning on with a blank/black screen despite charging?

Hello, in 2025 I just bought a Brand New Apple Watch Series 5 44mm (released in 2019) that is still sealed with Apple's characteristic black peel seal. However, this Apple Watch cannot be turned on at all, with no battery indicators whatsoever, neither green nor red. The display is just black/blank, even though I've tried force restarting by pressing both buttons simultaneously (If your Apple Watch won't turn on or won't charge - Apple Support).

I have already charged this Apple Watch with the charger that came in the box for a full day. The body of the Apple Watch feels warm as if it's charging, but still, there are no indicators other than the black/blank screen. I have also tried charging this Apple Watch with another Apple Watch Series 7 charger, which is already USB-C model, but still, the Apple Watch body is warm without any indicators and only a blank/black screen.

I contacted Apple Support to claim the warranty, but there's another issue because this Apple Watch is still new and cannot be turned on, so the 1-year warranty from Apple hasn't activated or started yet. Therefore, I cannot claim the warranty.

The question is, is there damage to the battery so I have to replace the Apple Watch Series 5 battery? Because I cannot claim the warranty provided by Apple, I want to repair it myself. However, I'm not sure if it's because the Apple Watch Series 5 battery has been sealed in the box for 6 years, so it no longer has any power at all.

[Re-Titled by Moderator]