Electrical battery drain fault

[justray]

Hi folks

A problem I’ve had with my C6 since I bought it two years ago is an intermittent battery drain which I’ve tried all sorts to trace. It’s getting steadily worse and none of the ‘standard’ techniques have traced it yet.

The dealership I bought it from replaced the battery after reading battery issues on the log but that was a ‘get it out the door’ fix. Subsequent log reads mention battery but nothing else. Often the car will sit for a week staying at 100% then hours later it’s at 10% before the auto shutdown arrests the drain by selectively shutting stuff down (I think) allowing it to always start.

Today was different though. It was 100% this morning then 50% by lunchtime, went to start it and …. nothing. All the indications looked normal but the starter didn’t turn. Tried a couple of more times before leaving the ignition on for a think. In front of my eyes the 50% charge reduced to 10% in 60 seconds – some drain for a battery of that size I’d hazard a guess! After a couple more tries it started and the battery charged slowly as normal. I had to be somewhere so didn’t get chance to apply gloved hands to cables to check for excess heating but that’s gotta be starter circuit or something big surely – any thoughts?

2007 Avant S-Line Quattro

[MarkTM]

Anything electrical been added, modified or repaired in your ownership (or indeed previous)?

Ask as adding of anything (e.g. radar detector/ bluetooth call system/new heated seat element/ aux power) can result in a drain.

Also have you had the battery itself tested...as that could be a duffer

If not I had the alternator fail on my 07 quattro at 105k miles, first it was the alternator regulator, it was sending charge to my battery but not enough, then it was a spindle failure on the alt itself.

[Akash]

One way you could try and get to the source is to see if any current is drawn from the fuses that should be off once the key is out. I know the ciggy lighters run with engine off, car locked so ensure nothing is plugged in that could drain it.
And then it's a case of identifying what fuses should be dead once car is locked and see if any current is drawn.

Also I see you have an avant - have you checked for any water damage/leakage in and around the MMI panel from the rear washer pipe?
There was a case on here where he had the fault and due to the MMI unit being damaged, it was causing the drain.

Again pulling the fuse for that if one exists would hopefully narrow that down.
The battery monitor s/w might also need updating for the module

[justray]

Thanks so far guys....

Car is stock, nothing changed at all. Batt was changed by PO for same snag I think but not checked recently so needs looked at I guess. For the amount of grief it's had I can't believe it's still going!!

Re fuse check the fault is so intermittent I could be there forever but yes, next on list.

Avant recall was done but I stripped it all out myself & dry as a bone with no water marks.

Hmmmm

[Alan02]

Try checking with an ammeter, at battery, preferably an amp clamp type would be best. It will show any current drain, bear in mind Canbus needs a minute or two to shut down once power turned off.

[gupsterg]

IIRC you'll know when CAN / car gone to sleep is when the hazard light switch is not lit.

It maybe pertinent to also lock car and view hazard light switch to see if car does enter sleep mode.

[justray]

Thanks again guys, local small Audi garage reckons some places install new batteries at 50% charge which the car expects is 100%, causing all the related problems. I remain to be convinced but have now externally charged the battery and await the next installment!

Additionally, the thing only starts four times out of five, regardless of the battery state - sheesh! I'm thinking it might be related but probz something like the clutch pedal microswitch. Give me strength...

[dan2485]

If you suspect the battery then take it a auto electrician who can check the battery capacitance.

This is simple test with a specialist tool that take a few minutes, it will say if the battery is no good or not.

This the type of tool needed

Ring RBA50 - 12V Digital Battery Analyser for Lead Acid Batteries RBA50 (http://www.tantronics.co.uk/acatalog/Ring_RBA50_12V_Digital_Battery_Analyser.html)

[apole]

Hi there,

I'd do a couple of things here.

Firstly get the battery tested, could well now be past it as they don't last forever and fail much sooner if they are discharged.

Next I'd pop the 3 fuses in the brown fusepanel on the RHS of the boot. The 3 you are after are for the Nav, tuner and amplifier. Check your handbook as to which ones these are.

OK you won't have these working like this but it will tell you if one or more of them are taking power when they should be off. Quite a common problem and was in mine. If that stops it happening then you need to either replace the bits that are faulty, or power them via an ignition switched relay.

Finally if you are able to get a VCDS scan, check the battery manager section and see if it has coding. Also check the size of battery fitted in AH terms is the same as the PR code says it should be from factory, if not you need to recode this correctly.

Hope this helps.

[MarkTM]

Ray, we have the same year car, since my last post on this thread I've had my alternator changed again.

Over a week I was getting over and undervoltage messages from a VCDS scan, I know that the battery is fine as it's brand new (and tested)

It turned out to be a failed rectifier and brushes on my alternator, to confirm, any decent battery shop will be able to test the output of your alternator which should be an unwavering 14.4v at idle.

As the weather gets colder we put more strain on the battery with heating etc...have you found it's worse in colder temps?

[justray]

Dan, Apole & Mark - only just seen your posts, many thanks! Will get round to trying them...

Latest update folks - Audi had the car for three days and tried to charge me £500 (another story) to find nothing. I'm now suspecting the meter that measures the battery voltage but no idea where it is - any ideas?...

[barnesautos]

I liked what @apole has suggested , the can-bus can remain awake one minute and then sleep the next . He has pointed you in the right direction in my opinion .
We had very similar issues on the top spec Mercedes , amplifiers , tv tuners , dab radio tuners all causing battery drain intermittently.
Also one to watch is the can-bus being water logged , shorts out the high and low circuit and causes similar issues .

[justray]

Update (it's been a while!):

My particular problem was a new battery that hadn't been 'coded' to the car. The car needed to know the batt make & model to ensure it was happy......which mine wasn't.

I called the original dealer I bought the car from who said my local idiots (Highland Audi, Inverness) should have thought of this!