This happened with the wife's mk7 TDi estate last week, loads of warning messages on the dash & pinging & binging away, so I scanned with VCDS and it showed loads of faults, but was acting oddly, some modules not reading, etc, I checked the battery voltage and it was 12.1v which is low and I know some cars freak out with low voltage.
She does lots of short journies, using stop/start, lights & heaters on, etc, so high load and not much driving to charge. It also turns out that she was sat in the car with the kids with the ingition on and engine off, so basically flattened the battery and triggered the warnings, women!
I charged it overnight with my CTEK and used the reconditioning mode to juice it up properly, it's been perfect ever since.
Will monitor to see if the battery is on it's way out, how much was the new AGM out if interest?