So here are the last 3 days, out of the car battery results. I couldn't fully charge the battery the begin with as I was busy, but I did that few days ago while leaving it in the car, almost same result too, but now with proper data:
12.7v --- 17th --- 90%
12.5v --- 18th --- 60%
12 3v --- 19th --- 40%
10.6v --- 20th --- 0%
Looks like the battery is toast.
It didn't drain voltage as much out of the car, than in the car, but either way by the 3rd day, the battery went completely flat and had no starting power at all.
I'm on my way to buy a new battery.
Possible cause:
I got the battery from recommended Tayna website few months ago, could be battery was damaged from factory, but could've been that the battery been kept a bit tilted in the car. Oh, wait for it, it's gonna be good :O Since I've had the A2, for over 3 years, the battery always sat a bit tilted, which was a tad weird, but the car worked good electronically, I left it like that.
After <2.5 years that battery gave in, so I got this one from Tayna. Now 6 months later this is done as well.
So upon checking the boot a few days ago, I'd noticed, the reason the battery was tilted all this time, because it was sat on the rear holding bracket! Real OMG moment!
However fit the battery prior to my ownership, just left it on the top of the brackets, instead of unscrewing the 2 bolts and fit the sliding tray over the edge of the battery, so 1 side was sat higher. I'd noticed this when I bought the car years ago, but it was working and sat solid as well, so I moved on to deal with other issues.
Learning something everyday :/
The CCU shows a few fault codes related to door locks, I'm gonna look into that as well, but looks like the battery and perhaps it's positioning was the main issue.
I'm not sure that caused the 6 months old battery to go bust though, as the previous battery was working like that for years, also cars do park up/down hill and they'd still work fine. Any suggestion about that? Cheers