# What is the Battery Voltage Reading at Rest and Running?



## TregDad (Jan 30, 2004)

Hi all,
Chasing down a battery drain issue on my Treg. 
Can anyone that has a known good battery tell me what reading they get on their in-dash voltage guage with key in ignition at the start position, with all accessories off? Mine is reading ~11.5v. 
Also, what about when running, all accessories off? Mine is 13.5v.
What's yours?


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## TREGinginCO (Jan 4, 2004)

*Re: What is the Battery Voltage Reading at Rest and Running? (TregDad)*

I may be wrong, but doesn't the volt guage read the output of the alternator... not the battery????


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## TregDad (Jan 30, 2004)

*Re: What is the Battery Voltage Reading at Rest and Running? (TREGinginCO)*

yeah, when the vehicle is running. At rest - engine off, it is the battery output. So off you get an indicator of battery strength, and running, you get an idea of recharging.


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## ladytregdriver (Feb 7, 2004)

*Re: What is the Battery Voltage Reading at Rest and Running? (TregDad)*

mine is reading like yours.....approx 11.5-12v in start position....everything off--I did notice that it changed by .5 by turning the headlights on and off.....13.5-14 running.


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## SlotCAR (Nov 28, 2003)

*Re: What is the Battery Voltage Reading at Rest and Running? (TregDad)*


_Quote, originally posted by *TregDad* »_Hi all,
Chasing down a battery drain issue on my Treg. 
Can anyone that has a known good battery tell me what reading they get on their in-dash voltage guage with key in ignition at the start position, with all accessories off? Mine is reading ~11.5v. 
Also, what about when running, all accessories off? Mine is 13.5v.
What's yours?

- 12 volts - Reading it in the morning, after sitting all night
- 14.2 volts - No accessories on
- 14 volts - ALL accessories ON - Lights, Heater, Seat Heaters, Heated Steering Wheel, Radio etc.

*- SlotCAR*


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## Rickanns (Oct 25, 2003)

*Re: What is the Battery Voltage Reading at Rest and Running? (TregDad)*

I don't know what valtages my battery is putting out, but I just went through another low voltage situation with mine. All cold starts Wed night, Thursday, and Friday morning produced the System Fault Workshop errors. Ran it to the dealer Friday morning. They could not find any drain and said the battery was just weak? They charged it up and has been fine since.
Go figure?
Rick


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## dentmac (Apr 29, 2004)

*Re: What is the Battery Voltage Reading at Rest and Running? (Rickanns)*

A fully charged 12 volt battery should show 12.7V. Without the car started the gauge should read over 12 volts with the drain of the lights etc. Under that , either the gauge is off or you have a problem. With the engine running , it should be over 14 v.. This is the altenator output. If your battery has been flattened a few times, it is probably pooched.


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## TregDad (Jan 30, 2004)

*Re: What is the Battery Voltage Reading at Rest and Running? (Rickanns)*


_Quote, originally posted by *Rickanns* »_IAll cold starts Wed night, Thursday, and Friday morning produced the System Fault Workshop errors. 

Same here. Mines at the dealer right now. We'll see. I don't buy that the battery has just gone a little flat for no reason and just needs a charge to be all better.


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## shervinf (Sep 17, 2003)

*Re: What is the Battery Voltage Reading at Rest and Running? (TregDad)*

My car read 13.7 when the car is on, and depending on battery condition reads anywhere from 12.2 and up.


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## jinxegg (Oct 14, 2004)

*Re: What is the Battery Voltage Reading at Rest and Running? (TregDad)*

The volt gauge reads the charge of the battery in volts, engine running or not..
You need an amp gauge (amperes) to read the output of an alternator and we don't host that in our dash...
My 0,02 euro...


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## jderbis (Feb 2, 2004)

TReg Dad -- Same here, except my System Fault Workshop error included the need for a jumpstart, once late at night at the airport (2 wks ago) and again the next morning. After the second jumpstart I drove it to the dealer, who's had it for the last 12 days. After the first couple they called and said they couldn't figure out the problem yet, but had a 40 page printout of fault codes. Then today they called and said it was fixed. Supposedly they figured out that the battery voltage was low, and after charging it fully it has been fine since; the system fault workshop and all the other codes on their printout were supposedly caused by the low battery sending a signal and repeatedly resetting everything. Seems suspect to me, that they had no answer when I asked what was causing the low voltage situation to begin with. Now just waiting to see what happens next time it doesn't start.


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## PhReE (Sep 16, 2004)

*Re: What is the Battery Voltage Reading at Rest and Running? (jinxegg)*


_Quote, originally posted by *jinxegg* »_The volt gauge reads the charge of the battery in volts, engine running or not..
You need an amp gauge (amperes) to read the output of an alternator and we don't host that in our dash...
My 0,02 euro...

Your measuring two different things here volts and amps. BUT since the battery & alternator are wired in parallel, and the battery is NEVER (hopefully) going to have a higher voltage than tha alternator output when its running, your effectively seeing the voltage output of the alternator. 
Measuring the amperage (or current) is quite a lot more tricky and really cant be done that easily in a vehicle...


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## rbeamis (Jan 29, 2002)

*Re: What is the Battery Voltage Reading at Rest and Running? (PhReE)*

I hate to say this, but no car is exempt from this rule either foreign or domestic that I know of. Go to Costco and if they carry an Optima that fits your truck, buy it, and if you have two batteries (V10), buy two. All new cars come with bare minimum batteries just like the bare minimum speakers installed at the factory and both should be replaced ASAP. I suppose something exotic like a Bentley or RR might be an exception, but I'm quite sure Touareg and every other VW follows the rule. If you can't find the right sized Optima at Costco, buy a yellow top Optima at your local battery dealer, Interstate, I believe, sells them. Good luck.


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## TregDad (Jan 30, 2004)

*Re: What is the Battery Voltage Reading at Rest and Running? (TregDad)*

Well, got my egg back from the dealer tonite. They installed a new battery. No indication of anything causing a power drain. They indicated that the battery failed a load test and that the low voltage was the cause of the faults (gee, I already knew that!). Now it reads:
12.5 volts at rest, no accessories.
13.5 volts at idle, no accessories.
Turning on accessories (radio, heater, heated seats) causes about a 0.5 v drop on both.
Thanks for your help all, now I will keep on eye on that gauge a little more closely. Something tells me, this isn't the last of this issue. 
oh yeah, supposed to be 8 degrees tonite, brrr!


_Modified by TregDad at 5:01 AM 11-30-2004_


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## TregDad (Jan 30, 2004)

*Re: What is the Battery Voltage Reading at Rest and Running? (rbeamis)*


_Quote, originally posted by *rbeamis* »_Go to Costco and if they carry an Optima that fits your truck, buy it, and if you have two batteries (V10), buy two. All new cars come with bare minimum batteries just like the bare 

Good idea, but I think VW can keep replacing them until the warranty is out. Then I'll spend my own bucks.
It's too bad, it didn't used to be this way. My original battery in my 89 BMW M3 lasted 10 years, and I have 5 years on the "new" one.


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## jinxegg (Oct 14, 2004)

*Re: What is the Battery Voltage Reading at Rest and Running? (PhReE)*


_Quote, originally posted by *PhReE* »_
Your measuring two different things here volts and amps. BUT since the battery & alternator are wired in parallel, and the battery is NEVER (hopefully) going to have a higher voltage than tha alternator output when its running, your effectively seeing the voltage output of the alternator. 
Measuring the amperage (or current) is quite a lot more tricky and really cant be done that easily in a vehicle...

It was very easily done in older models. My 72 Mustang Mach1 has an Amp gauge in the middle cluster and the wiring is very simple, if you read the electrical scheme of the car.
Is just that later, having a battery voltage gauge proved to be more useful in providing information, as you may have a properly charging alternator but a bad battery that retains very little or no charge...
Moreover the voltage output of the alternator reaching the battery is never the same, as it is being managed by the voltage regulator of the alternator, depending on the battery status... http://****************.com/smile/emgift.gif


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