Audi A8 D3 battery questions

[QBee]

I have a 2004 Audi A8 D3. Great car, if it weren't for all the things going wrong with it.

The present problem is battery related.

6 weeks ago I have a whole catalogue of bizarre electrical faults, but in the end I realised that the Bosch battery in it since I got it was duff (would only charge to 10.4 volts, and then discharged to under 3 volts in 8 hours), so fitted a new Exide battery.

Thursday night the car alarm went off at 0345. Headlights came on, siren going off, car wouldn't respond to the key, wouldn't start, etc etc. Over the next 24 hours it clamped down even more, it had clearly decided that i was trying to steal it. This morning it was electrically dead, all doors locked except the one I had opened with the metal key.

This afternoon I have checked the battery - only reading 11.2 volts despite regular use of the car in the last six weeks, but maybe drained by the alarm episode, so I took it out of the car and put it on charge briefly.
Then decided to try it again before dark, popped the terminals on and hey presto, the car welcomed it's long lost friend, but there wasn't enough in the battery to start the car.

Qiuestions:

1. Do I need to get access to a VAG COM and link the battery to the car's ECUS?
2. What will happen if I don't?
3. Should it have started with 11.2 volts?
4. Do we suspect rodents? I live in the country and have had other car alarms going off at night this autumn, and cannot explain the battery drain.
5. Where would you go to get it checked over? I live in the East Midlands and work in Cambs.
6. What have I missed?

Thanks in advance guys

[richardracer]

Hi there,

My 2006 Audi S8 failed to start and gave me lots of funny errors both on the dash and when queried with vcds. I changed the battery and they all went away. No coding required, just fit and then start, then clear all the error codes with vcds.

Cheers

Richard

[QBee]

Vcds?

[ukdennis]

Actually, you will need to get the battery coded to the car's computer. Otherwise the car's battery management software will not function correctly, and give spurious "low battery" warnings with a new battery. Happened to me (2004 built A8 D3 3.0tdi) and my VAG indie was initially clueless about the need to do this.

[QBee]

ukdennis said:

Actually, you will need to get the battery coded to the car's computer. Otherwise the car's battery management software will not function correctly, and give spurious "low battery" warnings with a new battery. Happened to me (2004 built A8 D3 3.0tdi) and my VAG indie was initially clueless about the need to do this.

Mine is the same model, and this echoes something my TVR indie said (he did his apprenticeship with Audi) when I mentioned it to him. If I can get the car to start on Monday I will get it coded.

[Dr G]

Yes; genuine battery and get it coded. They have a power management module that causes all manner of odd faults if absent or not coded.

[Adrian E]

If the non-genuine battery is the right spec, go into the coding with VCDS and change the serial number for the battery by one digit - that'll be enough to force the battery control module to 're-learn' the state of charge

[s4tronic]

Adrian E said:

If the non-genuine battery is the right spec, go into the coding with VCDS and change the serial number for the battery by one digit - that'll be enough to force the battery control module to 're-learn' the state of charge

thats what I have done when I replaced battery on my s4 b8, fitted exactly the same spec plain branding Varta in place of VAG branded Varta and just changed last digit on the serial in the VCDS. No issues whatsoever and battery was charged to 100% over couple of hours of use over few days and seems to be keeping very good charge.

[QBee]

That's a plan then. Tomorrow morning I go to the local Audi indie and get the Exide Excell battery coded to the car. Previous was a Bosch, so I will just get them to specify the type and change the last digit by one.

Then up on the ramp and a quick check for rodent damage.

How or where do I check for battery drain? I have a multimeter, all the gear, just little idea......

[helix402]

https://wiki.bentleypublishers.com/download/attach...

[QBee]

Thanks helix - I will do some reading.

New Exide battery read 13.3 volts yesterday when I bolted it back into the car.
Car dead to the world this morning - key stuck in the ignition again
Multimeter read 1.8 volts this morning - I have a massive battery drain somewhere.

[s4tronic]

I read that one way of testing for battery drain is to plug a multimeter to the battery so you can see the current being drawn and then remove fuses one by one to see when the drain stops.