2.4 Audi A6 - battery dying slowly

[SlineQuattro24]

My car battery seems to be dying after a week or so and I’m just trying to find out if my alternator is dying or if I’m just not doing long enough journeys.
I replaced the battery after the old one was having the same issue, but that one was old and worn out. (Was losing half its charge even after being on a charger over night)
On idle with the stereo and heaters on, the battery reads 13.8v, is that low?
I only work 3 miles from home and takes 15-20 minutes to work because of school/rush hour traffic etc.

I am just trying to figure out if I have a weak alternator, or I’m just not running her long enough. It’s a manual 2.4 A6 C6 Avant S-line Quattro.

[Crasher]

Which make and version of battery?

[SlineQuattro24]

Can’t remember what the old one was as it’s gone now (Exide EA770 after some google imaging), but the new one is a Bosch s5(read 12.8 when I plugged the charger in so its full.. but battery indicator read 10%)

[swalker]

seems to be a thing these days, i wonder if it is short journey syndrome, these cold mornings all the electrics will be on not giving the battery a chance to fully charge on a short trip.
My own was the same - every few weeks she would need atop up, then i discovered i left my OBDeleven in the diag port, and the school runs kicked back, all is well again.
there was also a post recently where it came up that a certain vintage of software gave a low output current on the alternator memory serves me right. but 13.8V sounds about right.

if you changed your battery the car should have been re-coded, you can get away without coding if it is like for like, but if the capacity was changed the car would need to know.

[Crasher]

I put a Bosch S5 in Mrs Crashers Polo and after going flat in two weeks four times I sent it back and asked for a Varta, On Monday it was 4 weeks and a day since I started it and it just started which is still not brilliant and I can't see an excessive parasitic drain.

[c..corgill]

did you check the date of manufacture, mate bought a exide 80amp batt from ECP and it was a year old.

probley a load of rubbish but i find if i turn everything off and then turn car off it starts better next day.