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Discussion Starter · #1 · (Edited)
Thought I'd do a quick write-up on replacing the battery in an S5 4.2 since I wasn't able to find all the correct info in one place.

1) Buy a replacement battery. Surprisingly, for me here in Canada, the dealer was cheaper than aftermarket. I paid $240 for an OEM (Varta) replacement. Part # 8K0915105F.

2) Replace Battery - this is pretty self evident and takes 10-15 minutes. The only setting I lost was the clock. Favorite radio stations, one touch windows etc., were all saved.

3) Code new battery with VCDS:
- Go to CAN Gateway 19, then Long Adaption, then Channel 4, Battery Identification.

- There are three strings of numbers in the following order (Part#, Battery Vendor, Serial #). For example:

8K0915105F VA0 080388159X

- I replaced the last 10 digits with the updated serial # on my new battery.

A few observations:
- Interestingly, the battery reading in the MMI was about 30% before and after I replaced the battery. It wasn't until I reset the battery serial # with the VCDS that it went up to 100%.

- My thoughts are that the battery reading in the MMI was never meant to give a reading based on current state voltage (…like a voltmeter would). But rather it is meant to give an indicator of overall battery life span given the monitoring of various readings over a long period of time.

- Resting voltage for my original battery was 12.1V. The new battery is 12.6V.

- Its pretty crappy given newer battery technology like AGM or VRLA (check these out if you aren't aware of them...), that we have to pay twice as much for an inferior replacement battery given the unique shape. I guess thats PAR for the course with these cars.

Cheers
 

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So, if your battery fails and you are stranded, you would have to have the car recovered to somewhere with a VCDS to get going again?
 

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Discussion Starter · #3 ·
No - not exactly. A new battery will start your car just fine.

The theory goes...and there is lots of conjecture out on the net on this....that resetting the battery with VCDS will result in your on-board computer to manage the battery and electronics differently.

For example, before replacing my battery, the car would shut-off the ignition after 3 minutes if the engine wasn’t running to save power. This was the case until I reset the battery with VCDS (even with the new battery installed).
 

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No - not exactly. A new battery will start your car just fine.

The theory goes...and there is lots of conjecture out on the net on this....that resetting the battery with VCDS will result in your on-board computer to manage the battery and electronics differently.

For example, before replacing my battery, the car would shut-off the ignition after 3 minutes if the engine wasn’t running to save power. This was the case until I reset the battery with VCDS (even with the new battery installed).
I agree with this as I was in the same boat. I replaced my battery last week, I just changed the middle letters from MLA to JCB because the battery i got was an agm type battery. I left the first and last string alone.

But coding new battery does restore power options that was limited. This is because the BEM actively monitors the battery state and like it was said above, to save power, the BEM will start to shutdown the car to ensure a startup next time. This is also the case that a battery severely drained will cause damage to the battery as well as electronics in the car.
 

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Did you try to recode as stated above in #3 (just re-input the same info since your battery didn't change)?

If that doesn't take/work, do it again but change a digit in the serial number. (e.g. add or subtract '1' from the last number in the S/N.
 

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Hi guys. My battery died and I recharged the same battery and refitted. I now have no MMI. It powers up the home screen then turns off. Is there anything I can do to rectify this?
It's worth remembering that you don't need to disconnect the battery to charge it - as long as you use a good battery optimiser. I use one of THESE. Never use one of the cheap, uncontrolled, half-rectified chargers as the spikes will fry your electronics.

If you look under the bonnet there is a removable panel near the bulkhead concealing a stud marked +. Nearby in the engine compartment there is a stud marked -.

Simple. :)

I'm afraid I don't have a solution to your MMI problem but IanH's suggestion of checking the coding is very sound.
 

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It could also be that your battery is knackered and the car is only powering up enough charge for the vital systems.

Check the battery, there must be a reason it died? Winter's coming and you need to a decent battery for peace of mind. :thumbsup:

DRT's suggestion with the optimiser is excellent as one of those will tell you the condition of the battery. I've got an Optimate 6 and tried it recently on my van from work as it kept going flat on me and the lease company wouldn't change it. :wall:
Told them the readings from the Optimate and they changed it the same day! :2thumbsup:
 

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Thanks guys for the support. I have tried the recode for a new battery even though it is the same battery just to see if there is any change. I test then save but there seems to be no difference. I went to halfords as they do battery check for free and they said the battery is good. Vag com gives me the energy management code. I clear the code but it comes back as soon as i drive. I am assuming it needs some kind of coding to remove the energy management. Im no expert, what do you guys think?
 

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I battery tester told me my battery was good - turned out it was dead - the halfrauds type battery checks are not good enough TBH - IMHO buy a new battery
 

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Hi again. I called the dealer and they quoted £188.00 for a replacement battery. I usually find in the past that the dealer is much more expensive that anywhere else. Should I purchase this or can I purchase one from elsewhere that is just as good if not better? I have an automatic 2008 S5.
 

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Dartmin after posting I read your comments on a previous post recommending a battery on ebay. Would that battery be suitable for me? How do I know if my battery needs to be AGM? Is this for stop start buttons. If so, i do have stop start button.
 

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That battery is for the RS5

you will have AGM having the stop start

best to find the current part number - I suspect it is a 020 battery
 

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ignore the s5 that is bosch name - the important bit is the 020
 
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