Apple Watch Series 2 is not charging, is this the battery?

I have an Apple Watch Series 2 38mm that out of the blue stopped charging. Have tried it on 3 different chargers and on different outlets (in different buildings) so have ruled out anything other than the watch being the issue. It shows the long corded low battery screen when I hit the buttons on it.

It is completely dead so I cannot unpair it like many reviews say to see if it’s a software issue.

Before I purchase the tools, I want to see if this sounds like the battery or if this has happened to others on how they fixed it.

Any thoughts or experiences on this? TIA!