Series 5 Apple watch does not turn on
So recently I got a apple watch series 5 from a friend and asked me if I could fix it. The watch just never turned on or showed any sign of charging. I wanted to come here and ask if you guys think it is a battery or a motherboard issue? I mean, Its brand new but has not been charged for 3 years. Last night I plugged it in and still no signs. I also opened it up, and it looks like the battery is not swelling. Any ideas?