I'm not sure I'd worry about it over much provided you're not getting any low battery warnings and it fires up okay, especially as you don't use the start/stop feature anyway.
The start/stop in my car - a three and a half year-old 2.0 TFSI 190 - has hardly ever worked unless I've driven well over a hundred miles, yet in all that time I've only ever had one low battery warning, and it's never once failed to burst into life. There's nothing wrong with the start/stop; it's just that there isn't enough juice in the battery for it to work most of the time.
Am I bothered?
Nope.
Start/stop is a pain in the rectum anyway.
And this battery is one of those Moll EFB jobs which are spoken of so very highly on here, so it isn't even a decent AGM.
I do hook it up to a CTEK from time to time when I remember, but it never takes more than two or three hours to light up fully-charged.
It may well be that I'm constantly walking the tightrope of being stuck in the middle of nowhere with nothing but the dull click of a starter solenoid for company, but like all adrenaline junkies I live my life right on the ragged edge.
.