Welcome!
Yeah, 99% confident that is a dying battery and a new one will help you.
Anker and EnergyPal are two battery brands I have tried in my Note 4 and they both work really well. The problem with Samsung OEM batteries is that I'm not sure if Samsung is building them any more, and there are a LOT of fake "OEM" batteries out there that are not worth your money. I strongly advise buying from a trusted seller that has a return policy.
The EnergyPal one is still fairly new and the jury is out on real battery life (so far it seems on par with a slightly degraded Anker but it hasn't been through three full cycles yet), but for $12 it seems to be a good battery.