battery voltage

vwdsmguy

Veteran Member
Joined
Jul 5, 2004
Location
Syracuse, NY
TDI
2002 Golf black 5-spd
When I test battery voltage while the engine is running what should it be? I seem to remember it being in the 14 volt range. Is it higher as the revs go up? The Bentley didn't help or I just couldn't find info in there.
 

WildChild80

Veteran Member
Joined
May 30, 2016
Location
Nashville, AR
TDI
2001 Jetta TDI 2000 Jetta TDI 2000 New Beetle TDI ALL 5 speeds
Mine ranges between 14 and 14.4 depending on what accessories I have running.

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oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
14v, but it can vary slightly based on battery condition (state of charge, etc.) and the loads on the system.
 

WildChild80

Veteran Member
Joined
May 30, 2016
Location
Nashville, AR
TDI
2001 Jetta TDI 2000 Jetta TDI 2000 New Beetle TDI ALL 5 speeds
Mine ranges between 14 and 14.4 depending on what accessories I have running.

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That's assuming the cigarette lighter voltmeter is accurate.

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Dh4276

Veteran Member
Joined
Jul 22, 2019
Location
South Carolina
TDI
2006 Golf GLS TDI, BEW
You should have 14-14.4 v when the engine is running, if you are using a cigarette lighter meter, it should be fairly accurate (if it was calibrated correct from manufacture). The cigarette lighter on my 06 is hot all the time which means it is a direct connection to the batter except for the fuse.

If you are getting higher than 14.4 or lower than 14, I would recommend using a multimeter at the battery to verify(this can also tell you how far off the cl plug meter is) the voltage. If you reading are still outside normal range, you will want to get your battery and alternator checked to see if one of them is showing signs of age.


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eddieleephd

Top Post Dawg
Joined
May 27, 2012
Location
Asheville, NC
TDI
2002 jetta Wagon
Voltage should only vary a little bit, like half a volt. The voltage regulator maintains a constant voltage and the amperage will fluctuate more with load.

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ToxicDoc

Veteran Member
Joined
Mar 1, 2018
Location
Virginia, US
TDI
2001 Jetta, S7, .216
When I test battery voltage while the engine is running what should it be? I seem to remember it being in the 14 volt range. Is it higher as the revs go up? The Bentley didn't help or I just couldn't find info in there.
It should never be less than 13.2 for the typical voltage regulator or above 15, and even that's a bit high. 13.5-14.5 is more typical.

You have more amperage with a faster alternator so it can support a higher voltage. It isn't so much that the voltage gets higher with more speed, but that at lower speed it may not keep up with all the current draw you are using so voltage drops a bit.

Also, when the battery is drained/low, the alternator will be more putting out more voltage to charge that battery and it'll drift down as the battery's state of charge goes up.
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
It's also slightly temperature-dependent (since the battery produces voltage using, of course, a chemical reaction) so you'll find your readings are a bit different in the summer vs winter, or when it's hot in the engine compartment.

In general the regulator decreases the alternator's output voltage slightly as the temperature increases.

Just another reason why "what's acceptable?" is generally answered with a range of values rather than one single value, and why what's normal for one person's car may not quite be normal for another person's car. :)
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Heh, what really gets people in a pickle is testing these newer cars and their dynamic charging systems. LOTS of alternators get condemned when there is absolutely nothing wrong with them. All for fuel savings and emissions, albeit at the cost of shorter battery life... which I am not sure how manufacturing and recycling and transporting lead acid batteries more somehow is good for the environment, but that is the world into which we've legislated ourselves.:rolleyes:
 

Powder Hound

Top Post Dawg
Joined
Oct 25, 1999
Location
Under a Bridge, Crestview, FL, USA
TDI
'00 Golf 4dr White 5sp, '02 Jettachero 5sp, Wife's '03 NB Platinum Gray auto(!)
Well said.

Supposedly, the Bosch voltage regulators are set to 14.5 volts, but I haven't found one yet that makes it there.

Due to the use of calcium to strengthen the lead plates in lieu of antimony that is no longer used, the charging voltage must be higher than it was in the past (e.g. 40 years ago before the change to "maintenance free" batteries). Unfortunately, the manufacturers of voltage regulators are not so good at making the actual products match the claimed specifications. Batteries pay the price in shorter lifetimes. Makes you think an evil combination is at work. I don't think so, I think it is tolerated incompetence.

Let the rumor mill begin!

Cheers,

PH
 

B100

Veteran Member
Joined
Jan 7, 2003
Location
Berkeley, Eastbania
TDI
2003 Golf
My data point: 2003 TDI Golf, with mods. Have been seeing ESP and ABS warnings for several months, about intermittent voltage. Battery was good, and continuity to terminals on ESP and ABS modules was good. Replaced both modules (with items pulled from scrapped cars) but ESP/ABS warnings continued. Then Radio would cut out, and Trip meter and clock would reset at key off.

Last night, sober as a judge, I swear I saw 12.75 volts at engine idle at the battery with my Fluke DMM. Today, I saw:

12.64 volts key OFF
12.34 volts key ON
14.45 volts at idle, lights off, doors closed
14.35 volts at idle, light on, radio on, fan on
13.3 volts at key OFF, and falling from there... down back toward 12 something.

Is it my battery? It has 8 years and 55k miles, an 80 Ah VW battery from dealer.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Sounds more like a poor connection somewhere to me. Batteries typically do not come and go with voltage, they either work or they don't.

12.6v is nominal, 10.5 during cranking is normal, 14v while running is normal.

All the positive feeds from the battery and alternator go through the fuse link box atop the battery, accept for the big lead to the starter which goes straight from the battery post.

All the grounds from the battery and alternator are through the ground cable, which goes from the battery to the bellhousing bolt, with a stop at the body underneath the battery. ANY poor connections along the way, from either side (power or ground, remember, electricity works in a circle, hence the word "circuit") can cause all sorts of problems.
 

B100

Veteran Member
Joined
Jan 7, 2003
Location
Berkeley, Eastbania
TDI
2003 Golf
For what it's worth... three weeks ago I put in a fresh (manufactured 2021) VW 80 Ah battery, and I have not had any ABS or ESP or dash issues. The car mostly sits, gets some freeway time maybe once a week, and even on cold mornings after sitting for a few days, it starts fine and no alerts. It's early yet to say definitively, but it's looking like the old battery was part of the problem, maybe was the entire problem.
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
Batteries being more chemical than mechanical they wear different than other stuff. They must be tested for capacity via a load test or a specific gravity test. Voltage only gives a clue.
 

Uberragend

Well-known member
Joined
Feb 1, 2009
Location
Tulsa, OK
TDI
'02 Golf 2Dr 5M Indigo blue, '03 Golf 2Dr 5M Candy white
Both my 2000 Golf and my now 2002 Golf have consistently run between 14.4V (idle) and 14.6V (highway speed) for years. I have changed voltage regulators (easier then extracting the alternator), tested the voltage in different locations, and come to the conclusion that these cars operate just fine in that slightly higher range. I have a local shop that rebuilds starters and alternators, and they said it was completely normal. Neither car ever had battery issues at all, I use Interstate 94Rs, and their normal lifespan is about 7 years.
 
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