MP4.2+6.0

Amazing little clean up post change. I often lost only the date--not even the time-- in the display. Easy fix in MMI if it happens. You have to run windows all the way down, then up, with window switches held the whole time for the one touch open/close to work again. No lost MMI settings in general, no lost radio stations, no lost Homelink for garage door, no lost settings generally, etc.

No prep before changing. Just be sure the little wire also hooked to the positive terminal goes back on and isn't broken. It is not some kludge add on like it may look--it is actually factory and important.

aTOMic

+1 this was my first thought; is there a tiny wire going to the + terminal?
What is the battery voltage in the morning before starting? While cranking? After cranking?

Does your car have the belly pan on? If not, and your trouble began after driving in rain (if I understand correctly) then Hardened Old belt + H2O = quiet slipping = undercharged battery. Which causes all kinds of weirdness on these cars. They pull 2.8 amps just sitting there after unlocking and even 18A with ignition on not running. The alternator's output is so high that it's actually water cooled.

All due respect to MP+ (one of the top two "Gurus" on here), if you can reset the serial number, I would do so, rather than hope the car figures it out. One less variable in the equation. Hint: Complete your profile including your location and maybe someone near you will offer to help. It's a 10-minute job.

Also the much-vaunted BMS is not completely reliable; yesterday I left the key in the car (ignition off, but it still pulls power) for ~5 hours and it wouldn't start, just clickclickclickclickclick. The weird thing was that the radio and the interior lights came on after I first tried to start it, two things that are supposed to go off when battery V falls below a certain threshold, but it still would not start. BTW I know this battery was not coded to the car when installed and is >7 years old, including being left in the disassembled car all winter completely flat (I know, sorry) and presumably frozen. Topped off the electrolyte, charged with a "reconditioning" charger (dubious utility but slow charge & voltage regulated at least) and have had a year of trouble-free driving.I cannot recall for sure but i think it's Bosch brand, I'll get back to you.

Re water in trunk area; be sure the channels around the hinges are clear! The rather stupid design of the hinges and the routing of the wiring on the left especially can easily allow leaves to occlude the drains and then you have all that rain from the rear window and roof backing up and finding its way into the spar tire well and both rear side compartments. I carry a 3' long by 3" diameter tapered refrigerator coil brush I got at Wally's in each car, and a set of chopsticks (amazingly efficient tool for grabbing and removing the compost piles that can form there). Here it's shown in detail on my Passat but the A8L is virtually the same.




Welcome to the best D3 resource BTW!
-Tom

Berny9621

My A8, the weirdness continues...... I took it to the batteriesplus and he tested it and said i was showing 950 out of 900 uhhh somethings. Its a VW/Audi/Skoda battery, took it to the dealer because it was a month of free checks......same thing battery is fine. I have noticed that i am getting the Handbrake, Headlight Range Control, ABS, and ESP warning more often now. But usually goes away after sitting off for 10 minutes, before the stall it would only happen every couple times a month.
Is it safe to assume its just a weird german electrics gremlin? I have an 03.5 D3...I have gone to get that fault i mentioned above checked before, but as soon as i pull into the service bay it clears and the error disappears when they check it via VCDS.

dvs_dave

As others have said, don't waste time getting the battery tested, just replace it. Your symptoms are symptomatic of a marginal battery.

mishar

This part needs more attention. Bad battery can't cause this and start the engine in a minute. That water in the battery compartment is suspicious.

MP4.2+6.0

Unless you know the age of battery, personally I would shoot it and move on. Analysis paralysis at some point. If it is an Audi battery (or many others) it should have a date code on it somewhere. What is it? Beyond 3 or 4 years, scrap and move on w/ symptoms shown so far. Or, spend maybe 5x that chasing just what is popping up so far, before getting to repair costs.

Without better diagnostics, running out of ideas in general. Information remains pretty generalized. No, car should not just be accepted as having gremlins if maintained properly.

Backing up, you could have some basic wiring harness deterioration issues, but again not nearly enough info.

Two suggestions for right now:

Berny9621

Today it made an odd almost grinding noise and some smoke happened.
I cant turn off ECON through MMI, which living in MN; doesnt concern me.
Checked the battery acid meter on the Varta battery and its clear and dry, headed to batteries plus for a new one.
I had an Outback that would sluggishly remove the starter gear when the battery was taking a dump

Berny9621

Drains were recently cleaned and the plenum was as well

Berny9621

Got the battery checked and replaced at autozone....turned out it was loosing charge. Its a Duracell Ultra Platinum AGM battery, will the AGM part cause problems?

Jack88

As long as it's got matching stats, it should be fine. Hopefully that clears up your issues. As a side note, whenever the drains have been cleaned, it's a good idea to test them all one by one to make sure they are in fact clean and didn't just get the gunk packed in. Easy to check, and could save you a bundle of hassle later.