I bought a used battery off this guy on CL for $50!
He works for the bmw dealership and told me he tested the battery and it passed all tests. The reason why he is selling is because he needed to certify a vehicle and it won't pass bmw certification with an aftermarket battery (Diehard)..
SO I got a good deal on a good battery. I didn't plug in the vent tube though but oh well it works good no issues so far.