VONBOTTLE

So i bought my '08 S6 about three months ago, today and once about 2-3 weeks ago, i came out to a dead battery. Went to jump it with my A6 which is my backup car now until i sell it and incidentally has about a two month old battery, was dead too! - both cars have Interstate megatron batteries, the A6 battery is actually a replacement under warranty from about a month earlier because it wouldn't hold a charge....but back to the S6, i jumped it with my wifes car and drove it around for a while. Started it about an hour later and it was hard starting, an hour after that it was dead again....the A6, which i also jumped earlier was dead as well. The battery date in the S6 is 09/14, it is H8 size with 730 cca - question 1 is, are interstate batteries garbage? Obviously the frigid weather lately doesn't help.....-6 last night, but the 10 year old battery in my wifes car started fine. 2nd and more importantly, is there a minimum cca the S6 should have? The one in there is rated at 730, the A6 is 790......looking at batteries at autozone and pepboys, the ones that fit all had between 850-950 cca, and i can't find anywhere what minimum amps i should have - does anyone know? I'm going to where i bought the car to have battery replaced, but i'm not sure i want another interstate even if it is replaced under warranty. Another thing, when starting the car, it takes maybe 3 seconds to actually fire up after pressing the start button - is this normal for the V10 engine? And does the alternator light normally light up while starting? It goes out right when it starts so i've assumed it's normal, kind of like when the check engine light goes on while starting the A6 but goes out once started. I'd aporeciate any input - autozone's battery, a duralast i believe has 950 cca and pep boys has a bosch at 850 cca, so if one of those is preferable to an interstate replacement, i'd obviously go with one of them.....thanks for reading all this!

VONBOTTLE

I just looked at Interstates website and looked up batteries that fit the S6, S8 and R8, it showed for the S6 the 730 cca one and for the other two an 850 cca battery (H9 size), so maybe interstate has the wrong battery listed? You'd think all three cars would use the same battery no? Or at least the S6 & S8 would

FL C6.5 Avant

you have vag-com and can read what the system is doing? sounds like a parasitic drain (big one), or potentially the alternator is not meeting spec.
Don't have an S6, but I've not heard that the S6 uses an H9 vice the H8 for the 4F A6.
730 cca is light. is that an AGM battery?
After a lot of research, i deemed the east-penn battery (o'reilly's) the best direct AGM replacement. 92 A-Hr, 170 RC. 850 CCA. It is a group 49 (H8).

VONBOTTLE

No, don't have a vag....both times the battery was dead was on very cold mornings....i sure hope its not the alternator as o recently replaced that in the A6, i'm guessing you have to pull the engine on the S6?.....anyway, neither mine nor the available one are agm except for one bosch platinum at pep boys, and 730 does seem low especially since the higher cca batteries (850+) come up on a search for the S8

Wake96c4

I'm thinking you can put a much larger battery in. I replaced the battery on my 05 last year and went bigger than the stock battery, H8 (I think), rated at 900 CCA. The nice thing about the Audi that I'm not used to with GM vehicles is the battery tray is adjustable lengthwise.

It looks like if there's something bigger than the H8 lengthwise that it would fit. I believe there is still about 2" of adjustment left in the battery tray.

As for the dead battery, mine seems to be dead if I don't drive the car for more than 2 weeks. Last trip had the car sitting at the airport for 3 weeks while I was away on business. I came back to a dead battery and had to be jumped.

That's twice for me. The next time I think I'll disconnect the battery if I'm not going to drive it for an extended period of time.

wild

The 3.2 A6 Avant 2006 (and presumably the S6 V10) have power management programs within the engine computer to determine battery type and age, voltage and amount of charge the alternator should provide. When a new battery is installed, the appropriate info via VAG-COM should be put into the computer. This avoids unnecessary charging which would affect battery life. Would suggest you check with Dealer Parts Dept to get correct battery specs. Often same "Audi "battery costs slightly less at VW Dealer Parts Dept. For 3.2 A6 Battery, Part No:000-915-105-CE-DSP. May be worth spending a little more to get the proper battery because a lot of features depend on it. Also, mysterious/intermittent problems originate with electrical supply.

VONBOTTLE

Well battery was tested and replaced under warranty but upgraded to the larger battery that's spec'd for the S8 with 850 cca and 180 rc vs i think 110 for the other. Old Battery was so drained it took a jump box on front terminals and truck at the battery to get it going....,anyway, the car fires up a little more easily, doesn't sound like it's struggling to turn over as it did with the smaller battery, was a $35 upgrade charge

FL C6.5 Avant

nice.... 180 rc is awesome.