I'm going through a similar thing having just replaced my Varta battery a couple of days ago on my W12.
The only replacement I could get locally was a Yuasa Silver 110AH/900CCA from Halfrauds for £162
There was no BEM Code label on the Yuasa so I cheated when I coded the battery back in. Had a few errors which I cleared down but was left with ABS Control Module, Auto Dist Reg & Level Control/Steering Angle Sensor errors which wouldn't clear. Took it for a sort drive, tried again but no joy.
Slept on it and when I checked in the morning they had gone and I was able to clear them down.
Ever since I bought the car the o/s/r door handle has never locked/unlocked the car but the only error VCDS flags is the Rear Left Door Handle Touch Sensor?
Well and the usual two Rear Right & Rear Left Footwell Heater fault codes that have been there when I bought the car 4 years ago!
I did buy the o/s/r door handle a while ago now and had it painted but never got round to fitting it as I heard it was a bear to fit. Annoying as it would be the one I would often want to use after filling up with petrol, locking the fuel filler flap and wanting to lock the car to go in and pay for the fuel I had just pumped.
Sounds like I need to buy one for the other side according to VCDS?
-=Glyn=-