One for an auto electrician or Audi tech.

Our Audi has developed a slow current drain, it has only failed to start once however cranking has been slow on a good few occasions. I’ve changed the battery as the old one was 6 years old so would fail sooner or later, but unfortunately not the cause.

The battery will hold a charge for a fortnight with no use of the car, but the battery meter (which can’t be trusted) is starting to show a percentage drop. It was looking a little low the other day, I did an 20 mile drive but the car failed to start today. Are there any common closed circuit faults that cause a drain on an A6, thinking central locking solenoid, relay etc etc. I’ve used an induction type ammeter, not the most accurate in the world, but it was not showing much in the way of a current draw after the alarm went on.

Any ideas or good auto electrician recommendations?

thanks in advance

2 weeks with no use before it fails is a very small drain. Check for good connections on battery and chassis/engine earth leads, replace or clean as necessary. Energized relay coils usually show .25 amp drain. try using a clamp meter and see what shows up after the car has been parked and locked for a good ten mins this allows the car electrics to shut down. Now if there is a drain try pulling relays out till it goes off. Lastly driving around will not charge the battery if it is flat it ideally needs charging using a charger (4 stage if I was being fussy).

I’d expect a bit less from one relay to be fair – about 150mA, but that could be wildly inaccurate with some larger relays. And driving around for 20 mins should give you enough charge to keep your average power hungry electronics going overnight quite happily (I’ve run with sulphated flattened batteries many times lol) but of course a good charge will get you back to scratch and 20 mins will not supply enough for a 2 week stint.

To be fair, most modern cars will begin to struggle after 2 weeks lack of use – a completely charged 100Ah battery would be as flat as a pancake if it started off fine with 300mA constant draw. Seeing as most alarm systms and engine management electronics draw around 80-150mA in normal conditions, you’re looking at a 50% capacity drop by 2 weeks without faults, which will likely be noticeable though it should still start.

As above, I’d check connections. Also bear in mind that cold weather generally leads to lower battery voltages on even a healthy battery.

Ultimately, if you’re going to be leaving the car for multiple weeks you really do need to be leaving it on a maintenance charge or you’ll end up going through batteries like there’s no tomorrow.

Have you checked your alternator? Although this should show a warning light on the dash if it’s not working…

Your batterly should definitely last a lot longer. I have an A6 which sat over the cold period there (about 4 weeks in total) and it started no problem the other day.

How is an induction meeter (amp clamp) going to work on a DC voltage? Or is it one with a Hall effect sensor as well?

And have a look/ask here:

http://www.vwaudiforum.co.uk/forum/forumdisplay.php?25-A6-S6-RS6

I’d higjly recommend Andy at A for Audi. Based in Glasgow and has done servicing and repair work on our VWs and Audis for a number of years with no problems.

As well as being a great guy he’s substantially cheaper than main dealer

thanks all.
Think I will pick up a more accurate clamp meter to see exactly what the current draw is and if this varies. As you say I can then start pulling fuses and relays to see where the draw is. I would rather not go to a garage/auto-electrician if I can help it just due to the time it can take to weed out the problem. But that said, always good to get a recommendation as above.

I’ve been using Lorimar & Finlay/Prestige to service my Audis for fourteen years now. They are down in Whiteinch, just off South Street, and have always been up front about any issues they have found, and well-connected enough to ask other specialists about things they cannae quite determine the cause of.
Hope that helps.