Surest bet is a factory battery, at least that's what I decided when changing my wife's Q5 battery. The main thing seems to be that the battery characteristics are the same as OE, because at least on the Q5, the charging is monitored by a current sensor on the negative cable clamp, rather than just having the alternator supply a regulated Voltage.

 

I'm sure you replaced the battery at this point, but wanted to reply with my experience if anyone else is researching. I recently replaced the battery on my 2014 Passat 1.8 T Wolf with an Autozone Duralast gold, H5-DLG. Fits perfectly, and no issues nor warning lights. And I was able to borrow a socket wrench extender from the store that I forgot to bring along to swap out batteries on the spot. If I had a higher end luxury model like a Q5 or Touareg then I would agree to use a factory battery in an effort to avoid potential fault codes. Passat is not that finicky.

 

All you need to do on the higher end cars like the Q5 is to recode the battery serial number. Basically just telling the ECU that there is a new battery installed. It resets the charging parameters for battery degradation.