How do you actually know if a battery place is legit before letting them touch your BMW?

[rafaelbridges]

Maybe I am overthinking this but I have trust issues with car stuff in general after being ripped off once. My 520i needs a new battery and I have been sitting on it for a week just reading and comparing because I do not want some guy poking around the electronics without knowing what he is doing. Every place claims to be the best, all have five star reviews, and half of them probably just reset the fault codes and call it a day. Someone told me the proper process involves registering the new battery to the car so the charging system adjusts, but how do I verify a shop actually does that instead of just saying they do? I saw a page where you can visit this page and read about the process, which was more detailed than most, but I still want real feedback from people who paid for it. Do you ask for proof of coding, watch them do it, or just hope for the best? Also how long before you know if the job was done right, is there a way to tell within a few days or does it only show up months later when the battery dies early.