Cost for replacing battery

[Pitosalas]

My 2011 3-series needs a new battery. I took it to the local BMW dealer (USA) and they said, grandly, that it would be US$500 (about 350 British Pounds!) Shocking. When I probed I was told that the battery is not an especially costly part, it's the installation that's so costly. Because they have to "register the battery with all the various components of the car, and if you don't do that the car won't run right." When I asked further what would happen if I went to a non-dealer who worked on foreign cars, they said that this could be done but it the car would have some unspecified problems. Is this a lot of nonsense or can someone confirm this? Thanks!