I've been around these parts since 2005 and I've seen a lot of "What Battery?" posts: CD has chimed in multiple times recommending Dealer sourced 55AH or 66AH batteries, Others like Walmart's Group 26, many pros/cons on red top and a fair share of praise for Interstate and DEKA. Searching on the term "Battery" here on the FAQ has not been extremely helpful. I've been using a 50AH BMW branded battery 61-27-7-567-181 for about 4 years and after an 8 week period of storage with no battery tender and a 1600 electric clock, this battery is toast and will no longer take a charge.
If you've purchased a standard 2002 battery (front location) in the last few months/years and are happy with the results, please reply with the brand, size and where you purchased it. If you know of a useful old FAQ thread that I can revisit, please post it here too. I'm going to purchase new batteries for both of my cars and want to make a good choice. Thank you, -Ben