i had my left side battery replaced about a year ago and i watched the shop (not a dealer) do it. the starter battery was not disconnected, the hardest part seemed to be lifting the battery out (fits tightley in there and isn't feather light).
Best Battery for Volkswagen Phaeton
As for the battery choice, I'd personally opt for the Varta. The main reason being the service life you have received from the original battery. I wouldn't worry too much about the Varta's lower rating as the original has seemed sufficient over approximately 6 years and most Phaeton owners are reporting excellent life from the original batteries.
Jack on my visit the battery was also replaced. Part# 000-915-105-CE. They also replaced two modules that were causing a drain on the battery.
The VW service called yesterday (I took my car in that morning) and stated the battery (driver side) was bad, and was replaced ($347, if not in warranty). Other battery OK.
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