Facelift Removing and replacing battery

Mikeso51

Registered User
My battery is perfectly ok, but I would like to temporarily remove it, and put it back a few hours later. Does anyone know what the consequence would be in terms of error messages, fault codes, etc. On my last car (VWPassat) this would throw up various error messages, but a short drive would clear them. Is it the same with the A3? I don’t have VCDS, and I want to avoid a trip to the dealer to have fault codes reset.
 

mikemod

Registered User
It should clear all the codes once you drive a bit.

If you connect a PP3 9v battery across the battery terminals, before removing the battery, it has enough to keep everything stored, obviously don't try to start it :smiley:
 

Phil-1

Well-Known Member
Regional Rep
It looks like the battery on my A3 is on its way out. Wife had a flat battery after work this evening. Can I just get a replacement battery of the same spec and fit it myself?


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Sean6211

Registered User
The A3 8V with start stop comes with either an EFB (Enhanced Flooded Battery) or AGM (Absorbed Glass Mat) battery, you can use either one. However, you should also ensure that the new battery coding/type is updated on the Central Electronics module using VCDS, as there is an intelligent battery monitoring system which needs to know when a new battery is fitted to ensure correct charging behaviour.
 

Matty_S3&S5

Registered User
When you reconnect/replace the battery (PFL 8V anyway); start the car and you'll get the Christmas tree dash and errors in the DIS. Turn the steering wheel to full right lock, then full left lock and re-centre to clear/reset the airbag and some other errors (cant remember which off hand).
Then drive and all should settle down.
 

Svenedin

Registered User
I read an article (in German) about whether it is strictly necessary to code the new battery. The conclusion was that it wasn’t necessary but only if the new battery was the same spec as the old one. I will look for the article (google translate does a reasonable job).
 

Sean6211

Registered User
There are a few views on the necessity of coding a new battery. Apparently as the battery ages, the charging system increases the voltage slightly to compensate for the higher internal resistance. If a new battery is installed without recoding, the charging system continues to apply the higher voltage to the new battery and thus shortens the life span. Also when I replaced my old EFB with an AGM, I had to recode it as AGM charging curve is different from an EFB.
 

Svenedin

Registered User
There are a few views on the necessity of coding a new battery. Apparently as the battery ages, the charging system increases the voltage slightly to compensate for the higher internal resistance. If a new battery is installed without recoding, the charging system continues to apply the higher voltage to the new battery and thus shortens the life span. Also when I replaced my old EFB with an AGM, I had to recode it as AGM charging curve is different from an EFB.

That makes perfect sense. Actually this is something I was looking into because I had a flat battery recently. My current battery is EFB (the car has start/stop) but I was considering upgrading to AGM which I had ascertained would need coding (which is why I haven't done it because I can't do the coding).
 

Sean6211

Registered User
Depends on the brand of the battery. Varta which is OEM for VW and Audi tends to clearly indicate EFB or AGM on the various batteries.
 

Sean6211

Registered User
11.9V resting voltage is very low, a healthy battery should read 12.4-12.5V and an almost dead battery reads 11.8V (0% state of charge).

Looks like time for a new battery, as your's seem to be nearing end of life.
 

Svenedin

Registered User
This morning I put a volt metre on my battery and it showed 11.9v when I started it it dropped to 9v. When running it’s charging at 14.7v. Is this correct?



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Charging sounds correct. Battery voltage is too low. One episode of flat battery doesn’t mean the battery is necessarily worn out. I’d charge it fully and see if it holds charge. If not then new battery
 
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Retroman

Audi A3 2010 Sportback 2.0 TDI 170 (CBBB engine)
Never seen anything substantive to confirm that it is necessary to "code in" the new battery to the ECU other than for the ECU to receive a service history of the actual date it was changed. People say that the ECU is so clever that it makes ongoing calculations as to how much charge the battery can retain based simply on the age of the battery - really? Can it tell the difference between brands, quality and length of guarantee? :whistle2:
 

Retroman

Audi A3 2010 Sportback 2.0 TDI 170 (CBBB engine)
This morning I put a volt metre on my battery and it showed 11.9v when I started it it dropped to 9v. When running it’s charging at 14.7v. Is this correct?
11.9v is less than 25% charge - with this to suddenly happen with the onset of colder weather, I would be content to bet £10 that the battery is on the way out :sorrow:
 

Sean6211

Registered User
Actually, it would not be too difficult for VAG to implement all that algorithm into the battery monitoring system. The fact that the system is already capable of measuring current going in and out of the battery for the life of the battery, as well as charging, rest and cranking voltage, not to mention the impedence of the battery all the time, it would not be difficult to have a fairly accurate model of battery aging and effects of sulphation.
 

Sean6211

Registered User
When you connect the battery charger, clip the positive lead directly to the positive terminal. The negative lead you need to clip it to the large steel bracket on the bulkhead just behind the battery, as this allows for the battery monitoring system to account for the charging current. If you hook it directly to the negative terminal, you effectively bypass the battery monitoring system.
 

Phil-1

Well-Known Member
Regional Rep
When you connect the battery charger, clip the positive lead directly to the positive terminal. The negative lead you need to clip it to the large steel bracket on the bulkhead just behind the battery, as this allows for the battery monitoring system to account for the charging current. If you hook it directly to the negative terminal, you effectively bypass the battery monitoring system.

Thanks. I guess that’s what the bracket was for but thanks for confirming it


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Svenedin

Registered User
Never seen anything substantive to confirm that it is necessary to "code in" the new battery to the ECU other than for the ECU to receive a service history of the actual date it was changed. People say that the ECU is so clever that it makes ongoing calculations as to how much charge the battery can retain based simply on the age of the battery - really? Can it tell the difference between brands, quality and length of guarantee? :whistle2:

I think if replacing like with like it is good practice but perhaps not always essential. If replacing with a battery that uses a different technology (EFB/AGM) or different capacity then it is essential.

https://stevesorensenmechanical.com.au/blog/battery-registration-and-programing/
 

Phil-1

Well-Known Member
Regional Rep
Update.

I got a smart AGM battery charger yesterday and left the car in charge all night. This morning it started all ok and the battery showed 12v standing, 11.9v starting and 13.1v when running. Think it might just have needed a good charge.


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Retroman

Audi A3 2010 Sportback 2.0 TDI 170 (CBBB engine)
This morning it started all ok and the battery showed 12v standing, 11.9v starting and 13.1v when running. Think it might just have needed a good charge.
I'd keep in on probation and keep it on the watch list. A good condition, fully charged battery should be reading 12.6V+ and when the engine is running 13.5 to 14.5V. A battery showing 12V could be up to 75% discharged.
 
Update.

I got a smart AGM battery charger yesterday and left the car in charge all night. This morning it started all ok and the battery showed 12v standing, 11.9v starting and 13.1v when running. Think it might just have needed a good charge.
It looks as if it still might.

Either that, or you need a new one. 12V when standing is less than a 50% charge, and if the battery is sound you'd expect it to be holding more than that after a full night on charge. A fully-charged battery in good nick should read at least 12.6V, and ideally just over 12.7.

If it was me, I reckon I'd put it back on the charger for 24 hours then disconnect the charger, leave it for a couple of hours more to settle and then put the voltmeter across it again.

If it isn't showing (and holding) north of 12.6V, it's probably on the way out.

Edit - this post crossed with Retroman's while I was doing it, but if nothing else it shows there are at least two of us thinking along the same lines.

.
 

Phil-1

Well-Known Member
Regional Rep
Another Update:

So after being on charge over night then driving it for 80miles on Sunday this morning it started fine the wife drove the 4 miles to work and everything was ok, come 4 O’clock and it just turned over and started.

Looks like it’s not holding it’s charge


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Mikeso51

Registered User
Classic signs of a failing battery I’m afraid. Worth shopping around for a replacement. There are lots of online suppliers offering next day delivery, and you could save a lot of money. I’ve used Battery Megastore and Tayna in the past for Varta batteries, and they have been excellent value.
 

Phil-1

Well-Known Member
Regional Rep
Classic signs of a failing battery I’m afraid. Worth shopping around for a replacement. There are lots of online suppliers offering next day delivery, and you could save a lot of money. I’ve used Battery Megastore and Tayna in the past for Varta batteries, and they have been excellent value.

Thanks.
The problem is the wife has the car and I’m working 200 miles away

Just signed up with Green Flag in case it leaves her stranded

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Retroman

Audi A3 2010 Sportback 2.0 TDI 170 (CBBB engine)
Euro Car Parts is offering 45% off batteries at the moment which makes them competitive given that their alleged "normal" price is high. I replaced my battery back at the start of November when they had a similar "Halloween" discount - I liked the fact that I could reserve online and then pop around to my nearest depot and pick it up over the counter. :smile new:
 

Phil-1

Well-Known Member
Regional Rep
Euro Car Parts is offering 45% off batteries at the moment which makes them competitive given that their alleged "normal" price is high. I replaced my battery back at the start of November when they had a similar "Halloween" discount - I liked the fact that I could reserve online and then pop around to my nearest depot and pick it up over the counter. :smile new:

Andrew Page are doing the AGM battery for £170


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