Weird issue starting with battery and now screen

[slash_lucky]

I bought my Iphone 6s plus new from ebay and used it for about 7 months.
Last night when I left it charging and unplugged after 100% battery, within 20 min without usage, the battery dropped to 50% and when I recharged it, it went to 100% as normal but again dropped to 45% within 30 min without usage. This morning, when i booted my phone after charging it, it shows apple logo and then I see something like this. Can someone please tell me if I need to replace batter, screen or both?

Thank You