New battery voltage?

[Mawcus]

Been chasing down some various problems and decided to get a new battery. 7 year old battery was working fine but checked voltage after sitting over night and it was a little low. One of the problems ive been having was flickering dash and headlights. Figured i was due for a battery so i got a new Interstate mega tron 94r H-7. Brand new battery had a voltage of 12.49 right off the shelf. Checked old battery with car off after it had warmed up and it read the same 12.49v. Not too happy about spending $200 on a new battery when the old one seemed to work fine. New battery didnt even cure flickering lights. Just want to know what voltage to expect from a brand new battery.

 

[meerschm]

http://autorepair.about.com/library/weekly/aa101604b.htm

that voltage seems ok.

voltage depends on state of charge.

but 7 years sounds like a good long life.

I would now look for ground or connection issues.

 

[Lightflyer1]

That is what happens when you start swapping parts out without defining what the problem is. You waste money buying things you may not need. So you bought a new battery and still have the same issue. You were probably due a new battery soon anyway so no real loss there. Next time trouble shoot and find the issue before buying parts. Have you checked and cleaned all of your grounds and connections? That can be done for free. A battery not being charged should have a voltage of about 12.5V +/-. In the car with the alternator charging it about 13.5V +/-.

 

[Mawcus]

That is what happens when you start swapping parts out without defining what the problem is. You waste money buying things you may not need. So you bought a new battery and still have the same issue. You were probably due a new battery soon anyway so no real loss there. Next time trouble shoot and find the issue before buying parts. Have you checked and cleaned all of your grounds and connections? That can be done for free. A battery not being charged should have a voltage of about 12.5V +/-. In the car with the alternator charging it about 13.5V +/-.

Here's a link to my troubleshooting efforts which so far haven't solved problems
http://forums.tdiclub.com/showthread.php?t=450317
New battery had 12.44v after car sat for 9 hours at park and ride while I was at work. Seems low to me but from what I've been reading seems acceptable. According to one chart 12.44 is between 80-90% state of charge which seems lame to me for a brand new interstate battery.
Anyway back to the drawing board

 

[jettawreck]

I always charge a new off the shelf battery before installing it.
Maybe time to look at your alternator output and if your drives are short enough you may not get enough charging time. Although, if you went 7 years on the last battery unless sometihing went south lately, normally it must be sufficient.

 

[Lightflyer1]

There seem to be quite a few electrical suggestions over there you didn't try or respond to. I would try those.

 

[Mawcus]

What am i missing?

 

[Vince Waldon]

Well, for one thing...the voltage reading of your new battery has sat for 9 hours is probably not all that meaningful. A voltage reading while the car is running and some load applied...headlights, heater fan, etc, will give you a better idea of charging system health. Since your issue seems to be flickering lights it would be good to track down an analog meter that will help you see if the voltage while running is perfectly steady.

 

[nutdriver]

Resting battery voltage will also vary with ambient temperature. What was the temperature when these readings were taken? The flickering dash lights also don't really sound like a bad battery to me. Is the car starting ok?

 

[Mawcus]

Temps were right around 45-50. Car starts fine. I think im just gonna have to chase down a loose wire or connection somewhere.

 

[Drivbiwire]

Resting battery voltage won't tell you a thing.

It's the voltage when under load that counts!

Even more telling is the voltage it sustains under load after a specified period of time.

A battery with good voltage may be a defective battery when it fails to sustain a minimum voltage after supplying a load.

Generally the battery has to provide not less than 10.5Volts after a load of 80amps of continuous load for one hour. If it drops below 10.5Volts, the battery is defective.

FWIW, a starter on a TDI only draws about 200-220 amps when starting...

In theory, the OEM 80Ah battery should provide 10.5 volts after 16 minutes of sustained cranking. That works out to about 300 amps draw from an 80Ah battery.

As the battery gets older, the time the battery can sustain the load drops.

You will NOT be able to detect this aside from a very gradual reduction in cranking rams which you will not detect by ear.

Rule of thumb, after 5 years of use, the battery should be replaced with a new one.

 

[nutdriver]

A typical battery test consists of three readings.

1. Resting voltage - tells if the battery is charged but not whether it can start the car on a cold day. A battery should either be rested awhile before testing or to first burn off some of the surface charge by pulling a small load or turning on the lights for a couple minutes. Optimal battery voltage at 40-50 degrees should be slightly over 12.5 volts approaching 12.6.

2. Charging system voltage - Another test is the voltage with the car running and perhaps some load on the battery system. Normally 13.6 - 13.9 volt range. Other vehicles run up to around 14.2. If not the car is not properly charging the battery.

2. Load test - that Drivebiwire describes is by far the best way to ultimately test a battery. I load test all my batteries as winter approaches.

To the OP, I would not feel bad about replacing this battery after 7 years of use. You got more than a reasonable life out of the original battery. I am delighted if I can get 4 years out of my batteries in Kansas. I think your problem is most likely not being caused by the battery. I agree with meerschm.... maybe a bad ground or connection.

 

[Powder Hound]

...

I would now look for ground or connection issues.

This ^^^.

Personally, I'd prefer at least 13.9 volts measured while the engine in running. Otherwise, the battery may never reach a fully charged state.

Since the alternator is charging and the battery is delivering a proper supply of electron pressure, flickering will be caused by the low voltage at the device (dash computer/electronics) that flickers. So, I'd figure you have grounds to check. Start with the ones under the battery tray as well as the connections at the alternator and those fuses in the little tray on top of the battery.

If there's no joy there, then start pulling the covers under the dash and start checking all of them. Then you'll need to consult a Bentley to start chasing down other connections and ground locations. For example, sometimes people have strange electrical problems caused by something not obviously connected such as strange light behaviors caused by brake light problems.

Good luck,

PH

P.S. If you are ever in a hospital and you see 'Bosch' on any of the equipment they are using, GET YOURSELF TO A DIFFERENT HOSPITAL WHILE YOU'RE STILL ALIVE!!!

 

[DanEboy]

Drivbiwire,
That load test you mention sounds excessive to me.
Sounds like you're saying 80 amps for one hour!
Really??

 

[tadawson]

That's the exact definition of an 80AH battery, and any less is below spec, but not necessarily failed. For a new battery (the thread topic), it should definitely pass this test, at least at the correct test temperature (capacity falls with temperature . . .).

- Tim

 

[Vince Waldon]

Almost. The Ah spec is (most often for car batteries) taken over 20 hours.

Example spec sheet... note the 20 hour notation in the Ah rating column on the last page: http://www.atbatt.com/media/sku_pdf/Exide-Edge-Booklet.pdf

So, an 80 Ah battery was able to deliver 4 amps for 20 hours... 80 amp-hours.

One reference for further reading: http://www.dcbattery.com/faq.html

The thing some people forget when they grab their calculators is that it's not linear... a battery that can deliver 4 amps over 20 hours will not be able to deliver 80 amps for one hour. This is due to the chemistry of lead-acid batteries and is known as Peukert's Law.

One reference for further reading on Peukert's Law: http://all-about-lead-acid-batterie...amentals/peukerts-law-and-exponent-explained/

 

[DanEboy]

"An amp hour (AH) is a rating usually found on deep cycle batteries. The standard rating is an Amp rating taken for 20 Hours. What this means, say for a 100 AH rated battery is this: Draw from the battery for 20 hours and it will provide a total of 100 amp-hours. That translates to about 5 amps an hour. 5 x 20 = 100. However, it's very important to know that the total time of discharge and load applied is not a linear relationship. As your load increases, your realized capacity decreases. This means if you discharged that same 100 AH battery by a 100 amp load, it will not give you one hour of runtime. On the contrary, the perceived capacity of the battery will be that of 64 Amp Hours."
(Credit for this explanation goes to batterystuff.com)

 

[993er]

Interstate mega tron 94r H-7. Brand new battery had a voltage of 12.49 right off the shelf.

That is low off the shelf and should read 12.65V to 12.9 V if fully charged. The voltage depends on the battery chemistry.

With the engine running and at 2000 RPM, what is your battery voltage?