Battery very bad on my Samsung Gear S3

[rix042]

I bought this "used on ebay. It always charged to 100% so quickly that it wasnt that fine tho. I tried everything flashing ROMS everything differenct cables. The thing is i dont have any Warranty. i bought the watch for 175€ which is good. I can get my money back becuase i paid with paypal. But what is this i think the battery is dead. Im assuming that this Device just didnt got only used for "3days" as he said because this battery is done. He said its a gift from his ex.... im so angry asf i wasted 3 days of my life to try getting this **** working on..