Battery Drain Returns out of the blue.
 

This evening it appears that after 6 months the battery drain problem occurred again today, I have no idea what the cause is. Last time this happened was January, and it sorted itself out.

Car last driven Saturday, left Sunday. Drove to work this morning with no problem, left work this evening but the car did not start with its usual get up and go. Checked on MMI and saw battery sitting at 60%.

Went on a detour drive to get home, and arrived back with the battery meter on 100%.

Sitting at home this evening noticed the LED in the door had gone out. Went to car, keyless entry dead so unlocked with key remote button. Started fine, checked on MMI again and battery meter now sitting at 10%.

I've just been a 40 minute drive, battery back at 100% again so lets see what happens now. Also went round the whole car and opened and closed the boot and checked everything is closed properly. I'll pop outside soon and see if the car has gone to sleep, really weird.

The car is being taken abroad in a just over 1 week, could really be doing without the hassle at this point. I don't have the tools or even time right now to try and track down a parasitic drain. It will certainly get a good run in that time frame. Dorset > Hertfordshire > Folkstone > Calais > all the way down past Rouen and Caen to the Mt.St.Michel area.

I did do a quick scan with VCDS and the battery manager showed no issues until just before 5am today, and then during this evening it jumped quiet quickly right up to stage 6 at about 8.30pm. Stupidly I cleared the fault codes.

The car is only driven short distances for weeks on end, last time it did any meaningful distance was 150 miles just over a week ago. Since then its covered about 15 miles in 8 days with 2 starts per day except for Sunday when it was left.

Only thing I can think of is the click flap motor is back again, so this evening I once again run the output tests on the HVAC motors. They all seem to work fine except the known stuck one in the engine bay, so I attempted the basic settings which I know fails due to the stuck motor in the engine bay. All now quiet again after the rest of the motors learnt their current values.

Battery is a Varta and now 18 months old and was coded correctly when I changed it.

This morning no problem, battery still at 100% after being left for 10 hours so very puzzling.

I feel your pain.

I recently drove around France in my 8, and too was concerned about getting a flat battery. I took jump leads with me, especially as I had a cool box in the boot. On the ferry out I even left the cool box plugged in by mistake. D'oh!

Thinking of your issue, an intermittent fault, the worst kind in my book, would it be prudent to go one better than jump leads and invest in a jump starter?

While not a fix, at least you would have peace of mind to enjoy France.

I can't imagine what I'd have done if I couldn't start the car with a ferry load of cars behind me!

Did you use VCDS the previous day?
I have found that if I unplug the VCDS cable from under the steering wheel AFTER turning off the ignition instead of before, the battery goes down to 10% over the next few hours.

Maybe you hit on something, yes I had used VCDS whilst trying to sort the clicking HVAC flap motor, cannot remember if the car was off or on when I pulled the cable out. I also used it last night. Difference was that last night I unplugged the cable before turning the car off.

Should be a sticky somewhere maybe, reminding all to disconnect VCDS appropriately.

I didn't know of this likely issue till now.

It would be good if others could try this and get a consensus.

Interesting. Do you need to do something special when you change the battery? I had mine changed a few weeks ago, but I didn't know there was more to it than the changeover.

Yes you should code the battery manager to say you have a new battery fitted, if you fitted like for like then you can just change the last digit of the serial number and that will tell it a new battery is fitted to start the process of learning its capacity.

But don't worry the cars not going to go into meltdown if you don't.

You need to code the battery module so it relearns the characteristics of the new battery, for example discharge rate. Currently your 8 may start switching things off needlessly because it thinks the battery is going to die faster than the new reality.

http://wiki.ross-tech.com/wiki/index...ry_Replacement

If the battery has the same AH and CCA then you usually just change the serial number slightly to fool it thinking it has a new battery.