Correct/good alternator voltage for 2009 Jetta TDI???

Hello!

My car has needed a jump start twice in the last couple weeks. The battery is only 1 year old, so I took it in to Walmart & they said it tested good. The battery was rated for 730cca, and was testing at 646cca. They put it on the charger & got it up to 681cca.

When I got home, I tested the voltage with a multimeter. With the car off, the battery tested at 12.67v (seems fine). With the car running at idle, it tested at 13.8v with nothing but the DRL on & 13.5v with the A/C blower motor on.

That seems a bit low. Shouldn't the alternator be showing more like 14v even under load?

Is it possible that my alternator is under-performing & should be replaced?

Any advice would be appreciated.

You probably need a new battery.

Was the replacement the correct 72Ah unit? These newer cars are hard on batteries, and the heat really kills them.

I've also had strange problems with my battery/alternator. See my thread here. Hope it helps at least a little bit: http://forums.tdiclub.com/showthread.php?t=392065

13.8V is a fine charging voltage IMHO, particularly in the summer.

Your Walmart tester is estimating capacity...CCA actually involves cooling the battery to -20F or some such... so your capacity numbers are a rough guide at best.

A good test would be to measure the battery the next time the car won't start. If it's really low (below 12V lets say) you know your battery is letting you down... it's gone south or you have a rogue current drain.

If the voltage directly at the battery posts is fine you can start troubleshooting connection and grounding issues, potentially a starter problem.. although if it jumps fine the connections and starter are probably ok.

measure the voltage at battery with car running and lights on blower on high and anything else you can turn on. you might have to rev the eng a couple hundred rpm but you should still see the 13.8. if not your alt isn't putting out the amperage. Common for a dirty connection to allow voltage thru to measure but not allow needed amperage thru. but many people have had problem with amperage draw with car off draining the battery. Problem some have found is radio not going to sleep after the car has been shut down for several minutes. have to determine if its battery, alternator, or draining problem then go from there. good luck....

If you bought the battery at walmart and they looked it up in the book for you. they might have sold you the wrong battery. different then gasser battery.

oilhammer said:

You probably need a new battery.

Was the replacement the correct 72Ah unit? These newer cars are hard on batteries, and the heat really kills them.

Click to expand...

Thanks for the responses, everyone.

How important is the 72Ah rating?

The Bosch battery I've been looking at is only rated at 65Ah (called the company). It's 690cca / 850ca. Group size 48. How big a problem is that Ah rating?

I actually called Diehard, as well, and they said they do not conduct Ah rating on their group 48 batteries because it is not a deep cycle battery.

Yeah, you put the wrong battery in there, so it is probably dead. How important is it? Well, Volkswagen could have saved a LOT of money by putting a smaller battery in every car they built (adding up to literally MILLIONS of dollars every year). And they didn't. So, I would assume it is pretty important.

Like I said, these cars are already hard on batteries due to the [up to] 16 minutes after run time of the cooling fans, and all the electrical loads the car has (glow plugs, lambda sensor heaters, aux. cabin heaters, etc.).

Get the correct one in there, 72Ah, Interstate's number is MTP-H6, but you may find the local dealer has the proper one at a competitive price. You didn't buy a cheap car, don't assume you can get by with a cheap battery.

Agreed. Go to the dealer parts counter, have them look up your battery by VIN and done. The correct battery at a competitive price.

Having to buy a battery twice sure does negate the $20 saved when you bought the wrong battery the first time.

I know this is an old thread but it fits perfectly.

Battery life in my 2009 is running 1.5 to 2 years. Alternator voltage is 13.8v, just like the orginal poster.

Replaced my original battery with a group 48 Walmart battery. It lasted from Jan of 2011 to Sept of 2013 (1yr 9mo). Decided I didn't want to fool with it again so rather than take it back for a free under warranty replacement, I went and bought a Bosch H6 size AGM battery for twice the price of the previous Walmart Battery. (Gave the failed Wally battery to a friend of mine who has 3-4 VW's at any given time, along with the receipt and told him to get a free one for himself, which he did.)

So, the Bosch AGM was installed in Sept 2013 and is now showing signs of weakness (slow cranking). It's warranted for 3yr free replacement so I will be getting a new one.

I am beginning to agree with this thread that these cars are just hard on batteries. High underhood temps (if I park the car in my garage at 6pm, I can open the hood at 6am the next morning and still feel heat radiating from the engine compartment) along with the killer ambient temps here in the summer (110F to 118F is not unusual) just kills batteries.

(Just did a post edit) Noticed that the original poster lives in AZ too. I guess that seals it, it's the heat.

So...Arizona heat is hard on these batteries, the cars are not hard on the batteries.

However, I think as cars have become more aerodynamic, and makers have lowered the hood line/narrowed the front end, and have used up every square inch of space in the engine bay, there's less air able to move around various components. While underway, it's probably fine, but sitting, as you've discovered, creates a very tight heat-sink. This is all my opinion, of course, but it seems to make sense.

Sorry for your battery troubles. I'll be living in TX soon, so I might be sharing your pain!

tdiatlast said:

So...Arizona heat is hard on these batteries, the cars are not hard on the batteries.

However, I think as cars have become more aerodynamic, and makers have lowered the hood line/narrowed the front end, and have used up every square inch of space in the engine bay, there's less air able to move around various components. While underway, it's probably fine, but sitting, as you've discovered, creates a very tight heat-sink. This is all my opinion, of course, but it seems to make sense.

Click to expand...

Almost all true. High heat does kill batteries. Here in Las Vegas, you are lucky to get 3 years out of a new (high quality) battery. My OEM battery lasted 3.5 years, but I am lucky - We have covered parking places at work and I have a garage at home. My car rarely has to sit outside in a parking lot all day. The desert sun is brutal if you have to park in the open, under hood temps can easily exceed 150 degrees (F.) for hours on end. Combine that with 4% humidity and even the best sealed batteries will fail.

My only contention with your post is that TDIs can be a little harder on a battery that other cars. In the winter the battery has to have enough capacity to not only start the car, but also to power the glow plugs. A Honda or Toyota (with a similar sized engine) never puts this kind of demand on a battery.

Have Fun!

Don

P.S. For a cheap (& easy) battery load test, find someone with a DMM with a min/max function. With the engine cold, put the meter on the battery and tell it to record minimum and maximum voltages (usually this means push the min/max button). Then start the engine, and check the meter's minimum reading. If it is below about 9.6-10 volts - you need a new battery.

I am still on the battery that came with my 09 that went into service in July 09. Unlike Arizona, it seldom hits 90 degrees here, and in winter, the car is garaged in a space that remains above freezing. Temperature extremes are hard on batteries. In southern Egypt, a typical car battery lasts about one year. And my charging voltage in summer is typically 13.8 to 13.9 volts.

Bumping this once again.

Today I got my battery replaced because the old one simply died (seems that it blew all the cells and shorted internally).

I got Varta 77 Ah 780A. The car started right off.

I measured the voltage with the car running at idle (all accessories off) at battery terminals and it showed 13.79 V.

Is this acceptable? Shouldn't it be somewhere between 14.0 and 14.2?

it's fine. Does the voltage hold up OK when the accessories are on?

Haven't checked that but will do that tomorrow.
I'm planning to turn on the following:
-Headlights
-Fog lights
-High beams
-Cabin fan to Max
-Radio
-Rear window heater

Not sure why but I feel I'd feel more confortable if I'd see a steady 14 volt reading....

I'll report back

Anything north of 13.5 is fine... and it will vary a bit between regulators... and also due to ambient temperature. The regulator is temperature-compensated, because so is the chemistry of the battery itself.

On a normal summer's day one of my Jettas does 13.5, one does 13.8, and my Mazda truck does 14.4. All are well within what's needed to charge a lead-acid battery.

I think you're just fine.

it is important to keep in mind that there are a couple different designs for alternators and electric system voltage regulation in the cars.

my 09 has one which takes a pcm signal to set the desired voltage. I have the voltage displayed on my scangauge and it will read 14.0 or 14.1 sometimes, and drop back to 13 and a half or so later. (probably moves more than that, but the point here is that it varies depending on some preset logic, including demands for electric heat.....)

older ones can just have an internal temperature regulated voltage selection (needed since the battery will not charge at very low temperatures without higher voltage, which would overcharge when it is hot)

As promised, the update.

This morning the brand new battery is flat again. This is ridiculous. I hate this car.
Something is really wrong, way more than an alternator and battery

Seems like a fine time to give some coin to an Irish mechanic, who may be able to figure out what exactly is the problem.

I watched on my ten mile drive to work this morning, outside temp was 55f (13C).

voltage indicated via OBD was 14 to 14.1 on the drive, and by the time I stopped at work, at idle, bounced between 13.4 and 13.6.

You could have a loose ground, bad alternator, or something draining the battery, or more than one thing.

I borrowed a nearly dead battery. It started the car.
I drove to a local mechanic.

He measured the charging voltage (strange, this time it was around 14 volts).

Then the next step was to check for parasitic drain.

With the car unlocked, all accessories off, key removed, it drains about 1.5 Amps. This is footwell lights I think and some other stuff.

During the moment of alarm lock, it jumps but then settles back at ~350 mA.
30 seconds passes and it is 100 mA.
Another 3-5 minutes do pass and it is steady between 20 mA and 30 mA. Never seen it go to 40 mA.

"Buddy, your car is OK, just get a new battery" - the local Irish mechanic said.

I explained him that the brand new battery became dead this morning. I left him the car to investigate furhter.

Hell, this car is driving me crazy.... Not sure what's the prob.....

The car sat at the workshop over night. Surprise surprise it started flawlessly this morning. The mechanic drove it a few tens of meters, parked. It started also during lunchtime.

I took the car for a spin, returned back. We checked for parasitic load - 20-30 mA with alarm/doors locked. Now the mechanic really thinks I'm krank. I refused to take the car back and said I'm leaving it for one more night.

Upon my return we observed charge voltage of 13.57 Volts at the battery terminals with the car idle and headlights on. I've discussed with the mechanic. He measure the voltage drop across the positive alternator cable (one end of multimeter at alternator positive output, second end of multimeter at fuse panel input). The voltage drop is 0.14 Volts <-- any ideas if that is within norms? Anyone willing to take measurements on their car (MkV or MkVI Jetta/Golf)? Would really appreciate that.

Thanks

sounds normal. The lights are taking 10A or so, the ECU likely the same, plus any charge being replaced in the battery.
What was the drop the whole way from alt to battery? Fuses can go high resistance sometimes...

DPM said:

What was the drop the whole way from alt to battery? Fuses can go high resistance sometimes...

Click to expand...

By saying 'from alternator to fuse panel' I meant from alternator to the point on the underhood fuse box where the alt cable connects to (just before the 200 Amp fuse). Voltage drop from alt to here is 0.14 V.

I don't recall what was the exact reading from the alt to the battery positive terminal but it wasn't significantly different from the above mentioned 0.14 V.

I wonder what the voltage drop is on other MkV/MkVI cars, I just need to compare to something else..

The car spent second night in the shop. Strange but the battery wasn't drained!
We'll see what the news will be today.

Still, any ideas about the voltage drop on the positive cable from alternator to fuse panel?

tsingtao said:

I know this is an old thread but it fits perfectly.

Battery life in my 2009 is running 1.5 to 2 years. Alternator voltage is 13.8v, just like the orginal poster.

Replaced my original battery with a group 48 Walmart battery. It lasted from Jan of 2011 to Sept of 2013 (1yr 9mo). Decided I didn't want to fool with it again so rather than take it back for a free under warranty replacement, I went and bought a Bosch H6 size AGM battery for twice the price of the previous Walmart Battery. (Gave the failed Wally battery to a friend of mine who has 3-4 VW's at any given time, along with the receipt and told him to get a free one for himself, which he did.)

So, the Bosch AGM was installed in Sept 2013 and is now showing signs of weakness (slow cranking). It's warranted for 3yr free replacement so I will be getting a new one.

I am beginning to agree with this thread that these cars are just hard on batteries. High underhood temps (if I park the car in my garage at 6pm, I can open the hood at 6am the next morning and still feel heat radiating from the engine compartment) along with the killer ambient temps here in the summer (110F to 118F is not unusual) just kills batteries.

(Just did a post edit) Noticed that the original poster lives in AZ too. I guess that seals it, it's the heat.

Click to expand...

Oh Gawd...... The AGM battery is the wrong battery in a different direction. Unless your car came with an AGM, the alternator will not provide the proper charging profile for it.

I sure hate repeating myself:

Ol'Rattler said:

Agreed. Go to the dealer parts counter, have them look up your battery by VIN and done. The correct battery at a competitive price.

Having to buy a battery twice sure does negate the $20 saved when you bought the wrong battery the first time.

Click to expand...

But I guess you have raised the bar and paid about 3 times the price of the correct replacement battery and still have issues..............

American battery's are not rated in AH, so there is no direct equivalent. My last dealer battery was something like $120 and is about 4 years old with zero issues.

Are there any unusual security systems in the area you normally park, Henrick? Wondering if some unnusual RF interference could be (say) keeping the CANBUS awake. Likewise do you park on a slope- could a door or bonnet switch be triggering during the night?

DPM said:

Are there any unusual security systems in the area you normally park, Henrick? Wondering if some unnusual RF interference could be (say) keeping the CANBUS awake. Likewise do you park on a slope- could a door or bonnet switch be triggering during the night?

Click to expand...

That was the idea which is in my head last day...

As for door and bonnet switches - I don't think so. The car is being parked near a house where people live. Alarm going off at nighttime would have woken them up and they surely would have complained.

Now the CAN not going to sleep and/or bonnet & door switches thinking the door is open - would that drain a brand new battery to death? I don't think so. It would of course weaken it but not to mV readings on the battery terminals in the morning... Door/bonnet open results in dome lights on (in my case, only footwell lights as the dome light switch is in "0" position all the time. Footwell lights = 10 Watts of power, besides, they have a timeout of 20 minutes or so....

Okay.
So it has passed some time since the battery hasn't been drained.
Today I decided to swap the borrowed battery back to mine (the brand new one which was recharged).

Meanwhile, the local mechanic routed additional positive wire from alternator to fuse box.

I picked up a plastic battery box at local salvage yard headed towards my garage.

When I arrived, I popped the hood and checked the charging voltage with engine idling, radio on and fan at lowest speed. It showed 15.25 Volts. Yikes, a bit excessive? But hey, nothing has been done to the alternator, only additional positive wire routed!

So I removed the borrowed battery, installed plastic battery box, installed my new battery. While I was there I replaced the air filter element with MANN filter (it appears that the original one was 'Filtron' which is OEM from the factory - made in Poland. Hey, they started saving money and have added not so famous suppliers), cleaned up a few things here and there under the hood.

After that I took the car for a spin. I was measuring the voltage at the cig lighter with my multimeter while cruising in 5th gear at 2050 RPM. Steady 15.25-15.30 Volts. If I trun all the accessories on (rear window heater, mirror heating, fan to Max, main beams, front and rear fog fights) the voltage reads around 14.8 Volts.

Now all it seems that I had some voltage drop across the original positive alternator wire. Hope the charging voltage will drop over time and rest at the expected levels of no more than 14.5-14.8 Volts....

Thanks everyone for help although my original issue (battery drain overnight) is still mysterious and haven't been caught. Hope it never returns.

Now it seems my first problem is replaced with another one - too high charging voltage which isn't good either.

So the voltage is 15.2 Volts constantly at the battery terminals. on the alternator itself it is around 15.35 Volts. Can I jump to a conclusion that the voltage regulator has failed, order a new one and swap it out (possibly with alternator on the car)? Or should I remove the alternator and bring it to the shop to do deep diagnosis?

I would guess the regulator.

if you are comfy working on it, would try to change on the car, otherwise pull.