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Discussion Starter · #1 ·
I'm seeing 11.34 volts when running on the rear battery.
Both batteries were replaced within the past 3 years old and test fine and charges fine.
Factory sourced AGM battery rated for 860CCA and when charged with our Snap-On DTAC it finishes charging and tests at 868CCA.

After charging up and reinstalling, the vehicle starts fine for a couple days but then starts to throw MILs regarding glow plugs indicating a low starting battery.

Alternator is charging front battery and displays 14.3+/- volts when running.

Rear battery doesn't seem to ever be charged by the vehicle.
Help?
 

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I'm seeing 11.34 volts when running on the rear battery.
Both batteries were replaced within the past 3 years old and test fine and charges fine.
Factory sourced AGM battery rated for 860CCA and when charged with our Snap-On DTAC it finishes charging and tests at 868CCA.

After charging up and reinstalling, the vehicle starts fine for a couple days but then starts to throw MILs regarding glow plugs indicating a low starting battery.

Alternator is charging front battery and displays 14.3+/- volts when running.

Rear battery doesn't seem to ever be charged by the vehicle.
Help?
Goggle search for vw self study program 298 PDF. The Touareg electrical system design and function. Clear explanation of how the two batteries function, charge etc.
 

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Discussion Starter · #3 ·
Thanks. I was looking for that.

I put the DVOM on the battery and watched the voltage drop from 11.3 to 2.5 when starting the vehicle. The vehicle started quickly (most likely utilizing the front battery) but the voltage continued to drop after it started indication the glow plugs were remaining active and pulling voltage from the battery.
"Charging of the starter and onboard power supply battery:
The onboard power supply battery is charged continuously. The starter battery is charged via the second
battery/starter battery charging circuit relay J713. This is actuated by the onboard power supply control
unit J519. The normal charging time is 20 minutes. After this period the relay will open. If the starter
battery voltage drops below 12.8 Volt, a new charging cycle of 20 minutes maximum is started.
While the glow plugs are active, the relay stays closed."
If I correctly understand the above, the alternator should be charging the starter battery while the glow plugs are active. That is definitely NOT happening.
The wiring diagram on page 29 of the self-study is full of electrical contradictions (in reference to current flow through closed switches and connection wires.)
I will continue investigate, possibly an issue with the J713 & J581 switch.
 

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Discussion Starter · #4 ·
Ok, after much testing, I've determined that the front battery is weak and in need of replacement.
I'm not at work to load test the front battery but it's resting voltage is 11.2V or less. The ECPM will choose to charge the weakest battery which in this case is the front battery.
This explains why the rear battery is not being charged.
If/when I jump J713 (Second battery charging circuit relay) to force charge the rear battery the engine RPM drops as if laboring slightly as the alternator is now charging BOTH batteries.
I will test the front battery Monday when I'm back at work but I see no dates on it and its a genuine VW battery which at least means it's 3 yo.
 

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Personally, for the few extra bucks involved, I would always replace both batteries at the same time.
 

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Thanks. I was looking for that.

The wiring diagram on page 29 of the self-study is full of electrical contradictions (in reference to current flow through closed switches and connection wires.)
I will continue investigate, possibly an issue with the J713 & J581 switch.
You are right, there are mistakes in the picture, but I assume it is clear what is meant:
The high amp consumers like glow plugs are sourced from the starter battery- as well as the cranking motor by closing the battery connecting relay J581 during the start process. THIS stays closed (=connected) to prevent overload of the J710/J701 if THEY don`t work as planned AFTER the start procedure. That means for the charging cycle of the starter battery either:

standard:loading in 20 minutes cycles/ check/ load further or loadstop
OR
exception: beeing always loaded (because the 2 batteries stay connected via J581).

I logged the battery voltages with vcds - you can justify that (s. below) => so in each case your trunk battery should be loaded.

enclosures:
-measurement of the voltages during start, x-axis in minutes, after 4 minutes both batteries are charged higher (but always with the same voltage !)
-charging log while 30 minutes of driving, x-axis in seconds, you can see the drop down of the charging voltage (around 20 minutes) to check the reached voltage level and then restart charging for both batteries again- but on lower level as before

my recommendation: empty batteries are typically a symptom but not the root - we have a 190 amps generator which delivers "charge" in every situation (except aux heater use or extremly short travels). One starting procedure is less than 0.4 Ah (450 amps x 3 seconds) which is below 0.5% of your battery capacity...

I would assume a too high standby current caused by ecu`s not going into full standby. In my case the Kessy-sensors in the door handles were faulty, so I decided to disconnect the sensors from the system... now there is peace in charging levels & (my) mind :smile:

For your further investigation I would recommend a clamp meter for DC amp`s - I bought an addon kit for the Multimeter which gives a signal of 10 mVolts/ Ampere for around 50 bucks. Place the clamp around the ground connector of a battery (in front of the driver seat or in the trunk), both can be reached easily for a direct charge measurement. Check if charging of your trunk battery works at all- if not go upstream (J713..)

Additionally: check the standby current, should be less 100 mA, ideally around 30mA (mine was 200 mA with 2-3 A peaks each quarter hour)

Close all doors, shut down alarm system, wait >10 minutes for standby and read the multimeter through the window... your key should be some yards away and don`t touch the handles ! Alternatively lock the OPEN driver door by clicking in the shutter with a screwdriver so the car "feels" his doors locked- same procedure with the handles...

br
Mark
 

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A check for the charging part of the system:
Find the cable coming from the generator ending up in the emergency start contact under the hood (under red plastic cap)- runs below the windshield/closed to engine from right to left side- thickness like your small finger. Release it a bit out of its clips (not the srew) to put the DC clamp around it. Start the engine and switch on as much electric consumers as possible-lights, seat heatings/window heating/ stereo: at idle turns it should give you around 100 amps current.
In parallel measure the voltage drop between a contact point on the motor e.g cylinder head and the negative/ground emergency start point- this will give you a hint about your generator to chassis connection: readings should be less than 200 milliVolts, ideally around 100 mV to prove a perfect ground connection. If that fails check the cable, which is on the right side (in driving direction) roughly on mid wheel level between chassis and engine. You can only see it bottom up- open the srew and look for corrosion, clean up with sandpaper 600+ (carefully- no scratches allowed!) and rebuild. If thats o.k. you should have 100-150 amps between idle and 3000 rpm, if not- check the generator
br
Mark
 

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Discussion Starter · #8 ·
Thanks Mark. I have an amp clamp for my meter at work and will get a reading hopefully tomorrow. Lots of great info you've provided there.
Much appreciated.
 

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Happy to help- still warmed up from a fortnight (ending last weekend) of tackling my electrical gremlins- beeing lucky having "beaten the beast"

and: my 3 years old batterie-set assumed beeing "dead" works like a charm despite all the deep discharge cycles...

pressing thumbs...

br
Mark
 

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Discussion Starter · #10 ·
Mark,
I measured 70-90A flowing from the alternator to jump post attachment KOER with typical load items on (heated seat, heated steering wheel, HID lights, HVAC...).
I load tested the front battery again (fully charged) and it failed the test.
I haven't had time to perform voltage drop tests on the grounds and power cables yet but will.
I simply believe the front battery is due for replacement at this point.
 

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Be clear that the generator is only producing what is needed- so the max. amps measured correspond at the end to the connected load (don`t forget rear window heating, ALL seats, radio/amplifier, foglihts, brake lights...)- if the generator/regulator is working correctly.

What I do not understand is how you performed the battery load test - connected some bulbs to check how long it takes to discharge? Pls. clearify..
Be sure let the battery calm down after a fullcharge cycle min. 3 hours before doing a discharge "stress test", otherwise results are misleading.
e.g. my "supposed dead" battery (3ys.) was up`n running after some nightly recharges with ctek 5.0 including one "reconditioning" cycle

My german forum mates found lifetimes of batteries in their V10`s between (2)3 and 11 years- obviously depending on deep charge cycles and sometimes on climate/ garage conditions. At the end everybody with a really short lifetime found electrical problems causing constant discharging

Do you have news about the trunk battery ? Checked if beeing loaded at all? If not the starting procedure will stress your front battery additionally


br
Mark
 

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Discussion Starter · #12 ·
My shop has both a carbon pile tester and a Snap-On DTAC Elite. Due to the unfeasible battery removal (at that time) for carbon pile testing, I setup the DTAC and performed a diagnostic charge on the battery where it performs a conductance, voltage, connection test, and measures CCA/DIN/SAE, and then pre and post test(s) charges the battery. According to those results, the battery being rated at 860CCA currently is only retaining 435CCA at 12.58 volts, suggesting replacement of the battery.
The battery has been on the 12V 2A trickle charger (connected via jump posts) for the past 2 nights when I return from work (5pm) to when I leave for work (7am) (14hrs). I drive 20 minutes to work and the front battery never recovers the CCA its rated for.
The battery in this context is the front battery (under driver's seat). It's a genuine VW battery with a previous replacement date of approx 3 years ago according to the previous owner.

I'm feeling pretty solid on the this battery being due for replacement.
 

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Sounds quite professional for testing... It`s clear for me that you can`t ever reach back to the standard CCA level- thats a part of the age and critical below 60%. Replace and find a second use for the old one :) (garage radio or jump start backup ?)
I would look for the biggest capacity fitting mechanically under the seat..
Just popping into my mind: I measured 450 A cranking currrent from the front battery during start- trunk not yet tested

Looking forward for the trunk results and standby currents..
br
Mark
 

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Discussion Starter · #15 ·
Recent tests have indicated and verified rear battery is ok and front battery is in need of replacement.
Waiting until after Christmas to replace.
I'll post back then.
 

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Here's a video I made when checking the charging of the rear battery on our 04 V10:


-J
 

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Thanks for the video. Nice illustration of how to use Fluke 88. One note: isn't emergency dtart (where front battery is used to crank) triggered by a counter-clockwise turn of the key preceding the usual clockwise turn?
 

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Discussion Starter · #18 ·
Update:
After testing the front battery (under the driver's seat) and finding it had one-two dead cells and never fully charged up beyond 11.4v (when charged on the bench.) I moved the rear battery (that tested well at 846CCA @ 12.65v) to the underseat position.
I then purchased a new battery for the rear (starter) battery position, I used a NAPA lead acid battery part #BAT 7549 (http://www.napaonline.com/Catalog/Result.aspx?Ntt%3dBAT%2b7549%26Ntk%3dKeyword%26Nty%3d1%26Dn%3d0%26D%3dBAT%2b7549%26Dk%3d1%26Dp%3d3%26N%3d0.
Morning temps today in mid-PA FINALLY were in the 20'sF and voltages on the batteries overnight were 12.65v in the rear and 12.57v in the front prior to start.
I started the vehicle and the voltage dropped to 11.47v in the rear and held steady.
I did not see the alternator charging the rear battery after start but the front battery was being charged at 14.27V post start. This worried me because in the video above and the workshop manual it shows the alternator being cycled to charge the rear battery when the glow plugs are active.
I drove to church and back and when I returned I checked the voltage of the rear battery (vehicle off) and it was 12.72V which indicated that it had been recently charged by the car.
SO! If your rear battery seems to keep draining, best to test your batteries (Load, conductance, and state of charge) and replace as needed.
If the primary (front, under driver's seat) is failing, the vehicle will keep trying to charge it and "overlook" the rear battery... allowing it to die off.

Note: the front battery was is longer than the rear battery and subsequently wouldn't fit in the rear position, but the opposite will work. When sourcing batteries, I didn't find a separate listing for each location that showed a different battery. In other words, stores were listing the same battery for both locations.
 

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Update:


If the primary (front, under driver's seat) is failing, the vehicle will keep trying to charge it and "overlook" the rear battery... allowing it to die off.

.

Your assumption is not correct- the rear battery is charged independently from the front according to its voltage-level. Probably your charging relay does not work correctly or the impuls by the control unit for the relay works wrong. Pls. be also aware that it takes up to two minutes after cold start, until rear charging begins.

In the enclosed log you will find the voltages after a cold start - x-axis shows seconds: Around 2000 seconds the charging is dropped, voltage measured and after that charged again on lower levels.

With VCDS you see both voltages in control unit 9, block 007

br
Mark

P.S.: In my 08/V10 both batteries have the same size but different capacities- I buy simply the biggest capacity which fits. Just ordered a hawker 1350 for starting purposes after upgrading with a ctek dc-dc charger connected to my solar roof...

Just realize that I already uploaded the log in a former post- forgive me...
 

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