HELP: What battery do I need?

[AudiAlanka]

I need a new battery and everyone I spoke with has told me something different.

-The AAA guy told me I HAVE TO stay within 640 CCA
-Costco quoted me the cheapest but didn't know what a CCA was, not sure they know what they're doing
-The Audi dealership told me they recommend a battery with 330 CCA based on my VIN number
-My mechanic gave me 3 different (expensive) options that were and told me he has never even heard of a CCA as low as 330
-Walmart and Autozone also suggested different batteries.

I'm so confused!!! How am I supposed to know who is telling the truth? And what is my cheapest option?

My car is: 2009 Audi A4 2.0L Turbo Charged

[Luxus Panzer]

your car is a B7. Wrong Forum ;)

[Charles.waite]

Its actually a b8.

Regardless, I'm fairly certain your battery needs to be above 650CCA. Cold Cranking Amps. Its simply a measure of how much power the battery can dump into the starter at cold temperatures.

[old guy]

Whoever you spoke with at the dealership didn't know how to read the information on the OEM battery. The OEM battery is a pretty good unit. This past March I replaced the batteries in my '03 A4 B6 as well as my '09 CC VR6 with OEM batteries. I picked both of them up from my local VW dealership. The A4 battery was $130 and the CC battery was $160. Both were replaced as a PM measure as both were still performing strong with resting voltage of 12.4 and 12.6 respectively. Both batteries were 6 years old so I had no problem with a preemptive replacement.

The nomenclature on the OEM battery is a bit different than what you see in a US replacement battery. For example the OEM battery for the A4 is listed as follows:

640A EN/SAE 380A

The CCA is 640A but if you follow the US nomenclature or ask an uninformed dealership parts guy, he (or she) will tell you the CCA is 380A. Not true.

Unless the price difference is ridiculous I would go with an OEM unit.

[Charles.waite]

I have this one in my b6: http://www.amazon.com/Optima-8020-16.../dp/B006QH55WY

Works great. You need to use the included mounting bracket so that the factory battery clam can properly work and the battery doesn't slide around though. I threw mine out and realized later my mistake. Optima was nice enough to fedex me one for free though.

[old guy]

One thing to keep in mind when purchasing a replacement battery is that a really high CCA isn't always a good thing. I recommend picking a battery that matches the OEM CCA rating. As the CCA rating increases the battery longevity usually decreases. High CCA's are achieved by adding additional (thinner) plates to increase the reactant surface area. It makes for a good CCA rating but it will usually decrease the battery life and result in a lower RC (reserve capacity) rating. Reserve capacity is pretty important with ECM's that keep residual power supplied to multiple different modules. Here is an old but excellent thread with information from Audinaut that is well worth reading. It also helps explain the OEM battery rating system: Clicky click® A high RC rating is really more important than a high CCA rating.