Thanks a ton Andrew. After some further research, it appears that my OEM battery has an "eye" that indicates battery life. There's a green/black/yellow status -- yellow being the status that indicates replacement. Mine's still on black but I have a sneaking suspicion that it will turn yellow soon. The battery seems to struggle in colder temps (which it didn't do last year).
I don't know if you've seen this thread, but it's a great write-up.
If you don't mind, I'll reach out when the yellow status crops up -- I'm guessing in the next month or so.