Just wanted to share my experience with my battery install. My
original battery was manufactured in November 2005 for my 2006 325i. I followed a DIY from youtube except I disconnected some wires on the distribution box (don't know how he got the battery out of there with no problems). Also, there are two vent holes, so I used black electrical tape to cover the vent hole on the negative side. The vent hole on the positive side is in the exact position as the OEM vent hole.
I installed a Walmart MAXX-H8 battery which is identical to the OEM battery. It has a 3 year replacement warranty and a 2 year pro-rated warranty. I spent $119.00 for the battery and it was manufactured in August 2013.
I registered the battery by buying a $10 cable from e-bay and used free software (donations accepted) from a member on here, smooth1. Google/download BMWLogger.
If anything goes wrong I will post an update, otherwise figure everything is fine.
The DIY video is located here: