2009 Jetta TDI - Battery Issue?

I am thinking there is something wrong with the Battery in my 09 TDI. It provides excellent cranking power but if I use any accessories in the vehicle with the engine off for more than say 10 or 15 minutes, it will kill it to the point of where it wont even turn over or will not turn over fast enough to start the engine.

For example, I drove home from work yesterday (30 minutes all highway) with the alternator working wonderfully (14V on Scangauge)... Got home and was doing some work in the car. I had no key in the ignition, I only had the interior lights on and it couldn't have been for more than 20 minutes, I then turned the scangauge on and noticed the voltage was down to 11.6V, tried to start the car, it cranked over slowly and eventually just stopped cranking. Had to boost it with my pickup, after running the car for 10 minutes the car restarted fine. I cold start this car every morning (20F) and have no issues. It just seems to have next to zero capacity. I thought this was a 60AH battery!?

My question is, if I bring this battery to the dealership - will it fail a load test? It seems to provide full cranking power just not for any length of time. I also have aftermarket Stereo equipment in the car (two amps, 5 ferad cap, sub, deck) and I am 100% sure the stealership will attempt to blame the aftermarket gear the the battery problem... which is BS... It's connected properly and grounded properly and without the deck on the amps are unpowered. I kind of want to just bring them the battery and say "this is the battery out of my 09 tdi, test it" rather than bringing in the entire car.

hoeser said:

I also have aftermarket Stereo equipment in the car (two amps, 5 ferad cap, sub, deck) and I am 100% sure the stealership will attempt to blame the aftermarket gear the the battery problem... which is BS...

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RUH ROH. I'd say you're between a rock and a hard place.

Maybe you just show up with the battery and tell 'em the car is dead...you had no choice. See if they'll bite.

Otherwise, I'd say you're writing a check for a new battery. Batteries do fail, even new ones, Mr Hoeser

Have you (or can you) check to see what is being CONSUMED from your battery when your car is not on. Yes, it could be your battery, and probably is. However, if your amps are accidentally wired into the power source and if the radio is on, or perhaps you caught the dome light circuit and when they're on its completing the circuit to some of the power equipment, this could easily drain your battery. Another thought is, was the key in the ignition or not? That can impact some items being powered in the car. Was the key in the ignition and the seat heaters turned on? That will ZAP your battery in no time.

Does your Vag Com have the capacity to check "line load" to see how much power is being consumed, and / or just put a basic voltage meter on the battery without it being connected to the car, check your voltage. Then attach it to the car and check your voltage. It will drop some, but if it drops a LOT, you can KNOW something is sucking a lot of amps. Very elementary approach, but watch the meter and see how much it varies based on different activities with the ignition switch.

Also remember the car has an aux heater... I don't know for sure what triggers the heater to be on (other than temperature)... but again, it could be if the key was in the ignition and it was powering up....

Just a thought.

hoeser said:

... I thought this was a 60AH battery!?

My question is, if I bring this battery to the dealership - will it fail a load test? It seems to provide full cranking power just not for any length of time. I also have aftermarket Stereo equipment in the car (two amps, 5 ferad cap, sub, deck) and I am 100% sure the stealership will attempt to blame the aftermarket gear the the battery problem... which is BS... It's connected properly and grounded properly and without the deck on the amps are unpowered. I kind of want to just bring them the battery and say "this is the battery out of my 09 tdi, test it" rather than bringing in the entire car.

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when I was at the detroit auto show last year, I noted that the battery on the display JSW was only ~60Ah. I was wondering if that was only because it was a demo model. It's surprising to me that they put such a low capacity battery in a diesel. I wonder if there is enough room in the battery box for a larger capacity unit? I took a photo of that at the show. I will check and comment back.

Seems to me that a 5 Farad capacitor could pull a bunch of juice from the battery. I just don't know if that would be available to the starter (it may be "locked" into the amp with diodes).

I agree with DD- you are in a bit of a tight spot. I would just bring them the car and ask them to test the battery. It's still under warranty, right? If they give you a hard time about the aftermarket stuff, make them show you how it is connected in a way that would kill the battery. If they persist in their position, take it to an independant shop and have the battery load tested.

wesk is right- you should also check the battery for drain with an ammeter when you think everything is in a powered-off condition.

Yeah, I'll put an ammeter inline and have a look see. I don't recall having the key in the ignition, or if it was in the ignition, the ignition was in the full-off position. The car Stereo wasn't even IN the car at the time, the amps were, but they were off (remote turn on disconnected). The 5 farad cap should draw no current if the amps are unpowered.

60AH = 60 amps for one hour, in optimal conditions. In order to deplete even half of that much capacity in 15 minutes I would have had to have had a massive short in the system that would have melted any wire I've got run in that car? Maybe I'm wrong? It just seems like all signs point to bad battery. Maybe I'll pull it and test it at Parts Source in town here, I believe they have a free load tester.

i would also check the terminal connections on the battery and the alternator output. It may be that the alternator has a good output, but its not all getting to the battery.

hoeser said:

Yeah, I'll put an ammeter inline and have a look see. I don't recall having the key in the ignition, or if it was in the ignition, the ignition was in the full-off position. .

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I can't be completely sure about this - don't have schematics for the electrical... however, unless I'm badly mistaking, once the key is IN the ignition, even though it isn't turned on, the PRESENCE of the key DOES authorize (turn on) some circuits. Someone correct me if I'm wrong, but I'm pretty sure I'm not.

I absolutely know this to be true on a Chevy I own... and I in fact did accidentally drain the battery once as a result. So now it's standard procedure when me or wife pulls into garage to remove key from ignition and lay on dash....

Wes

Classic sign of a failed/failing battery. If key was off, no major loads should be on (seat heater, fan motor etc). Nothing else could draw enough to flatten battery in that time without blowing a fuse or burning something up. Unless the battery was failing. I've seen new batteries fail, but it is very rare.

Classic sign of a failed/failing battery. If key was off, no major loads should be on (seat heater, fan motor etc). Nothing else could draw enough to flatten battery in that time without blowing a fuse or burning something up. Unless the battery was failing. I've seen new batteries fail, but it is very rare.

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That is pretty much what I was thinking, any load big enough to drain a good battery in 15 minutes is probably going to blow fuses or burn wires. I did accidentally kill the battery 100% one day a few months ago, I wonder if that destroyed it... I left something on overnight.

Yes, taking one completely flat can ruin it.

Dan

hoeser said:

I did accidentally kill the battery 100% one day a few months ago, I wonder if that destroyed it... I left something on overnight.

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Ah, the plot thickens! Yep, there's yer sign. Discharging a lead-acid battery pretty much all the way can indeed kill it, unless its a deep-cycle battery (which ours ain't). I've had a few batteries that could survive two or three deep discharges and still retain capacity, but a lot of 'em won't.

The good news is, you don't have to worry any more about arguing with the dealership about warranty...since you know it was your fault.

Did you recharge it after you drained it? Driving for 30 minutes won't do it.

Is there a relay on the caps to make sure they don't charge when the 'system' is on? And are you using the stock headunit or one of your own? The reason I ask is that the stock unit will remain powered with the key off.

If you don't mind going to the stealership, they will replace it.

Did you recharge it after you drained it? Driving for 30 minutes won't do it.

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I drove it for about 8 hours, actually.

It's at the local stealership today, will be interesting to see what happens. They already began by treating me like I was an idiot.

Does anyone know how many amps the car will draw with the key off?

Well they replaced the battery, but also blamed the fault on my aftermarket radio.. the service guy even pulled me into a little room to tell me all about the huge favor he was doing me by replacing the battery, and boy was he condescending and rude. He indicated that my radio was "drawing power" - I asked how much, he said it shouldn't matter, it shouldn't draw any (wrong). He also said it was "drawing so much power it won't let the car go to sleep" - I asked him what he meant by "sleep" and he said it was a "generic term used to describe the cars "low power mode"".

I did check the power draw of the main 4gauge line feeding my amplifiers and 5 ferad cap with the radio off, it was about 25mA.

Was going to check the power draw of the deck itself, but couldn't find the fuse (the owner's manual is *horribly* incorrect).

hoeser said:

Well they replaced the battery, but also blamed the fault on my aftermarket radio.. the service guy even pulled me into a little room to tell me all about the huge favor he was doing me by replacing the battery, and boy was he condescending and rude. He indicated that my radio was "drawing power" - I asked how much, he said it shouldn't matter, it shouldn't draw any (wrong). He also said it was "drawing so much power it won't let the car go to sleep" - I asked him what he meant by "sleep" and he said it was a "generic term used to describe the cars "low power mode"".

I did check the power draw of the main 4gauge line feeding my amplifiers and 5 ferad cap with the radio off, it was about 25mA.

Was going to check the power draw of the deck itself, but couldn't find the fuse (the owner's manual is *horribly* incorrect).

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Condecending or not, they did you a favor by replacing the battery. ANY lead-acid, AGM, or gell battery will be destroyed by a single complete discharge. It causes a layer of sulfer to form on the lead plates which will result in it never working to any appreciable capacity again.

http://www.trojanbattery.com/BatteryMaintenance/Discharging.aspx

the draw before it goes to sleep (low power mode) is around .25 amps after you turn off the key, get out of the car and lock it. the car then goes through a phase for about a minute or so where it checks for successful alarm activation and other stuff. It also powers down interior lights and other items. At low power I think it gets down under .1 amp.

Ok. Since you didn't say directly, I'm going to assume you are using an aftermarket head unit. It would not surprise me at all if this is keeping the system from going into 'low power'/'sleep' mode since it may require communication via the CAN bus to the OEM radio. The only way to tell for sure would be to measure the parasitic drain on the battery after the system is shut down. This is not that easy to do since you need something that will measure the small amps and can be put in line with the battery prior to closing the hood. You have to close the hood to activate the alarm. And the alarm has to be active to get into low power mode.

It would not surprise me at all if this is keeping the system from going into 'low power'/'sleep' mode since it may require communication via the CAN bus to the OEM radio.

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It is an aftermarket head unit, and it is connected to the can bus via the PAC C2R-VW module. The system should not be attempting to reach the oem radio as I removed it from the coding on the CAN Gateway computer.