On mine, the main battery gave up so I fitted a new one, still no stop start.
Fully charged the small one in the boot still no stop start, turned the air con off, light went green. As soon as I turned air con back on, the light went yellow again.
Fitted a new small battery in the boot, stop start nearly always green, even within a minute from starting up, even before the temp gauge has moved.
Two new batteries means it’s back to new car state.
I got the car when it was nearly two years old, hardly ever saw the green light, it just got less green as time went on.
It was 4.5 years old when I had replace them, Ctek was no help either.
Stuff charging, fit new.