The battery in the Note 5 or any sealed battery will definitely degrade over time. My current warranty replacement is averaging 5 to 5.5 or slightly higher SOT. My previous Note 5, after eight months of very hard use, the SOT was 3.5 and dropping.
I can't stand sealed batteries and in the past, just popped in a fresh, new factory battery and kept the older ones as spares. I went on my way happy with a strong battery.
I carry extended warranty as well and at some time will have to go to battle once again with Verizon to get them to send me a refurbished phone, with hopefully a fresh battery.
Dealing with Samsung, I no longer do that! I absolutely hate their distasteful so called customer support. No wonder why the Note 7 failed! They have an ego so huge, the failed phone came back to haunt them.