BMW Repair: Replacing Battery, sears diehard batteries, plastic elbow

Question
I have a 2001 330i, whose battery is dead, checked by Sears. They tell me I can only get it replaced by the dealer. Is there any other option? Any other batteries that I could use that comparatively work just as well?...I am not quite ready to spend an arm a leg with the dealer.

I was told that a battery from autozone that is somewhat comparable with the same cca should suffice. I'm not sure how much I should trust that.

Answer
Anand BMW batteries are externally vented. On the side of the battery is a black plastic elbow and a vent tube that take the hydrogen gas to the outside of the vehicle and doesn't leave the gas in the trunk. What ever battery you decide on make sure it has this feature and the vent fits. BMW batteries are Good for about five to six years on average. They run about $120.00 retail. If you go to the dealer to have the battery replace they can clear any faults created by under voltage. They also are starting to carry AGM batteries. What is AGM do you ask? Absorbant Glass Mat technology is such that it no longer uses lead calcium plates. They have a much longer service life but are also more expensive to produce. They were introduced in some 2002 models with heavy electrical loads. I have never replaced one. The sulfuric acid is not loose and therefore cannot leak. They are black in color and the battery is totally sealed so it requires no vent tube. BMW regular batteries are white.
          I don't know if autozone batteries are any good or not. If you can find an Optima battery that fits I know that they are very good and durable. Each battery size are classified in group numbers. You have to find what group number battery fits the tray with comparable specs. No retailer makes their own batteries. They are all manufactured by big companies and rebadged an sold to retailers. BMW batteries were made by Douglas. Now they are made by Exide. I believe Sears Diehard batteries are made by Johnson Control, or at least they used to be. You should have plenty of info to make your decision.
-Evan