Battery charging issues

[Echo]

Hey guys,

I’m looking for some advise with my Audi A4 B8 2008 2.0 TFSI 104k miles. Car’s battery isn’t charging up as well as I’d expect it to and it feels like it’s getting worse lately. For a while I was hoping it’s simply because I don’t do a lot of long trips but last week, did a 4h long drive on the motorway and according to MMI the battery was only 30% charged after it. This is making me suspect that there’s something wrong with the alternator or charging system rather than battery or parasitic draw.

Things I’ve checked so far:

• Car battery is around a year old, Varta Silver Dynamic 77 AH
• I’ve taken the battery out to charge it up using a battery charger and it charged up fine, went to 12.6V and MMI recognised it properly
• I’ve coded in the battery using VCDS as per this guide
• No alternator/battery related error codes present but I can dump a full scan log tomorrow.

Today I thought I’d go outside and have another go and figuring out what the issue could be. When looking at measuring block for CAN gateway module, I noticed that the CAN gateway is requesting 15V from the alternator, but the measuring blocks are only reporting 13.3V which seemed quite strange to me. I checked the voltage between the jump-start points and measured 13.3V, exactly as reported by the CAN. 0.02 V between alternator housing and negative jumpstart terminal. I couldn’t see clearly at first where the alternator positive output terminal was but then figured out it’s the nut on the back side of it. Measured 14.8V between the alternator + terminal and negative jumpstart terminal which makes me think that actually the alternator is working fine but there’s an issue elsewhere. Found a 1.5V drop between alternator positive and jumpstart positive terminal.

I feel like I’m getting somewhere with this now – this 1.5V drop makes me think that there’s some faulty connection along the cable.
Any thoughts what would be the next best move? I’m thinking of either jumping the connection or looking and replacing the cables.

Thanks!

[Smac770]

https://www.audizine.com/forum/showt...with-new-cable

Do more measurements, confirm the actual point of voltage drop, amend that situation.

[Ringsby4]

Hey guys,

I’m looking for some advise with my Audi A4 B8 2008 2.0 TFSI 104k miles. Car’s battery isn’t charging up as well as I’d expect it to and it feels like it’s getting worse lately. For a while I was hoping it’s simply because I don’t do a lot of long trips but last week, did a 4h long drive on the motorway and according to MMI the battery was only 30% charged after it. This is making me suspect that there’s something wrong with the alternator or charging system rather than battery or parasitic draw.

Things I’ve checked so far:

• Car battery is around a year old, Varta Silver Dynamic 77 AH
• I’ve taken the battery out to charge it up using a battery charger and it charged up fine, went to 12.6V and MMI recognised it properly
• I’ve coded in the battery using VCDS as per this guide
• No alternator/battery related error codes present but I can dump a full scan log tomorrow.

Today I thought I’d go outside and have another go and figuring out what the issue could be. When looking at measuring block for CAN gateway module, I noticed that the CAN gateway is requesting 15V from the alternator, but the measuring blocks are only reporting 13.3V which seemed quite strange to me. I checked the voltage between the jump-start points and measured 13.3V, exactly as reported by the CAN. 0.02 V between alternator housing and negative jumpstart terminal. I couldn’t see clearly at first where the alternator positive output terminal was but then figured out it’s the nut on the back side of it. Measured 14.8V between the alternator + terminal and negative jumpstart terminal which makes me think that actually the alternator is working fine but there’s an issue elsewhere. Found a 1.5V drop between alternator positive and jumpstart positive terminal.

I feel like I’m getting somewhere with this now – this 1.5V drop makes me think that there’s some faulty connection along the cable.
Any thoughts what would be the next best move? I’m thinking of either jumping the connection or looking and replacing the cables.

Thanks!

Even Varta can prematurely fail,an auto elec can load test it in 5 minutes.It just may be the battery.Make sure you disconnect the neg terminal before the load test.
Our two Varta's both original oem fitment,one 11 years old tested 85% capacity last year,the other 9 years old 95%capacity last week.German stuff,mostly awesome.
EDIT- pos stop-start disabled via VCDS.......

[Echo]

Is the cable between alternator and the starter accessible at all?

[Smac770]

You can see the cable down on the bottom back right of the engine, passing through that metal shell. The problem is getting to the end of the cable where it's bolted to the starter. The cable from the TV22 block to the starter to the alternator is all one cable, and includes the lines from the T5l plug to the starter term 50 connection and the alternator VR connection. Which is why I disconnected it from the alternator and wrapped it up and ran a new cable from the alternator to the TV22 block.

[Echo]

Got it sorted today, battery charging properly now!
Solution ended up being exactly as described in your post @smac770

Couldn't see any damage or corrosion on any terminals or cables. Cleaned them up just to be double sure but ofc it didn't help. Added a 35mm² jumper wire and working great