Apple Watch logo blinks white to faded red while charging

I have an Apple Watch Series 1 which I didn't wear for almost 12 months.

When I put it on the charging stand, the Apple logo turns on white and like 1/2 second later it turns off, and even sometimes it turns off by fading into red.

What can be happening?

I already checked the charging stand with a different Apple Watch and it works fine.

Thank you for your feedback,

Luis