The Mystery death of my iWatch Series 1

I bought a Apple Series 1 online just for fun. I had another watch with a bad display and thought I’d use it for parts. First though, I have to try to fix it of course. I put a known good battery in it, hit the power button and…eureka! The apple logo appeared. It stayed lit for maybe thirty seconds then went out again and I haven’t been able to get it to do anything at all since. I have installed, reinstalled the battery, display, even tried a different charger. Any suggestions before I send this to the trash?