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Discussion Starter #1
Long-time lurker, long-time Porschephile, 1st time poster so greetings to all......

I know, from gleaning these forums, that this question has been asked before but without much in the way of a definitive answer.

I have owned a 2.7 981 for 8 months now and have just loved the car - it has been even better than I could have hoped for and my wife and I have accumulated 6500 trouble free and entirely enjoyable kilometers of spirited driving.

Back in September, I noticed my voltmeter showing higher than normal voltage [it previously showed high 13's to low 14's], with brief spikes into the 14.8 to 14.9 range. It happened enough times that I e-mailed the service dept. at the dealer - response - this is normal.

This continued, on and off, for several weeks although the voltage settled in the 14.9 range for the entirety of my driving. And these were not short drives either - always at least 45 minutes to an hour, 3 or 4 times a week. I figured I was driving long enough / far enough and often / hard enough for the battery to be fully charged and contacted the dealer again - same response - this is normal, don't worry about it.

Since October, the voltage has read 15.2 V constantly, never changing even after a 1.5 hour drive. Finally, I convince the dealer to take a look. The visit is very brief - about a half hour - they say the battery is a bit weak [reads 12.4 engine off on the gauge] but stress this is no problem and eventually the battery will be back up to full charge again. They send me on my way with no real solution apart from being told my car is operating normally and [if there was a problem] the car would send back a code or show an dash warning.

So [as of last week] the voltage has read 15.2 for over 7 weeks and, to me, this is troubling, implying the alternator is running 24/7 to try to charge the battery - but not being able to do so. And this is all while the car is regularly driven, driven at speed with higher revs and never short, start-stop trips.

I should also say that the car has been hooked up to the Porsche charge-o-mat for over a month, and reads green 15 minutes or so after any driving, implying full battery charge.

So, what do you think? Bad battery? Bad voltage regulator? Or, paranoid and just get on with driving the car? This has been affecting my ownership experience, as I prefer to be proactive, rather than wait for problems and don't think this charging behavior is as normal as the dealer implies.

Thanks for any help / advice.
 

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Discussion Starter #3
Just to be clear - the car has been on a trickle charger [the Porsche charge-o-mat] for a month, and the car did get driven very regularly when the problem began.
 

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While the battery might be weak, the voltage numbers are probably fine.

Sorry Lemon, but I think the normal AGM charging voltage is 14.7. not 14.3. The voltage (if it works they way the other Porsches do), will automatically rise in two conditions. First, if in sport or sport +, it rises. Second, if the the outside temperature is cold is rises. 15.2 is of no concern. If its its the range within your gauge, its OK, As long as its in subfreezing temperature, the voltage, while driving, might not drop down to 14.7. That has been my experience. I don't worry about it.
 

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In normal driving(no sport mode), my voltage has consistently read 14.3 or 14.4 volts. This is in relatively warm southern california.
 

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we get a constant 14.3 here is socal.. maybe that for colder states...i did not know about AGM.. you learn something new everyday..

thanks
Lemon
 

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normally a 6 cell battery should have 12.6 volt max 2.1 volt from each cell. The higher than max (12.6v) should be surface charge that is generated by running the alternator or by constant charger.
 

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In normal driving(no sport mode), my voltage has consistently read 14.3 or 14.4 volts. This is in relatively warm southern california.
we get a constant 14.3 here is socal.. maybe that for colder states...i did not know about AGM.. you learn something new everyday..

thanks
Lemon

And that is probably right. In the summer with 75 - 90 degrees. As the temperature approaches 32, things change. AGM batteries charge at 14.7. The cold, or snowflake setting for CTEKs, charge at 14.7 where cold is defined as below 41. You all got it easy in socal.
 

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And that is probably right. In the summer with 75 - 90 degrees. As the temperature approaches 32, things change. AGM batteries charge at 14.7. The cold, or snowflake setting for CTEKs, charge at 14.7 where cold is defined as below 41. You all got it easy in socal.
Chow as usual is correct.

But if you are finding after a full charge and then driving in Normal mode the voltage is not reading below 14V your battery is a problem. Mine fully charged reads 13.2 in normal. As the car in normal mode drops the voltage down and increases it only under braking. Energy recuperation system.

If you have fully charged the battery on the tender and then driven the car and the voltage is around 15V (in Normal) your battery has problems.

Do you use Auto Start Stop? this is a good way to tell. If your car refuses to do the Auto start stop and its been warmed up and you don't have AC max on. You have a battery problem.

From 25 years of Porsche ownership. One thing I can say is Porsche Batteries are [email protected]
 

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Discussion Starter #10 (Edited)
This is what happened on all the previous threads on this topic - no consensus.

My battery tender reads full charge minutes after being hooked up, but the voltmeter continues to read 15 + V, no matter how long I drive the car.

The dealership told me not to worry about my batteries state of charge and insist constant 15 + V was normal, even if it never drops. They didn't feel the need to do anything apart from insisting all is well.

So, what is the bottom line? Is 15 V normal for colder conditions or is it a case of my battery never reaching full charge? And, if the latter, does this imply that the alternator will run constantly and wouldn't this be very hard on that system?

So, I can take the dealership at their word or I can assume they don't know what they are talking about. That said, they have been so insistent that what I am seeing is completely normal, any more pressing and I will start to feel like a paranoid pest. I have made several phone-calls, e-mails and a service visit for this ''problem'' but I can't really see what more can be done.
 

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Do you use Auto Start Stop? this is a good way to tell. If your car refuses to do the Auto start stop and its been warmed up and you don't have AC max on. You have a battery problem.
This is a good point. I always have it off but if the car won't turn off, then the battery is not sufficiently charged.

Good find.
 

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I'm curious, what is considered the upper limit for voltage. I can see a voltage bar to the left of the 14.3V, but its tiny and there is no number that defines the upper limit.

As long as 15volts doesn't put you in the red range, I would say its within limits.
 

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Mine now reads 12.5 while driving.

Sometimes it refuses to Auto/stop.

981 bs. Wth.


Sent from my iPhone using Tapatalk
 

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Discussion Starter #14
I thought this would be clear-cut with only one correct answer but after hours of surfing the net for voltage readings, studying AGM battery literature, reading every post here on the subject and starting this thread, I remain in the dark......
 

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I think you're worrying about nothing. See this, in particular scatkins posts. Yes, I know its about a 991 but I am also fairly sure the charging systems work on the same principle.

Rest easy :)
 

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My voltage was at 15.1 with the outside temp at 40F.
 

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I thought this would be clear-cut with only one correct answer but after hours of surfing the net for voltage readings, studying AGM battery literature, reading every post here on the subject and starting this thread, I remain in the dark......
I too consider 15v charging (well below the upper red limit) to be completely normal in colder climates. Over here in 'Blighty' we dream of SoCal temps but it remains cold and miserable! From new my car was around 14.4 to 14.7v when picked it up a year last November and now it stays permanently around 14.9 to 15v. I too have fully CTEK AGM charged the battery and it still indicates 14.9 to 15v when fully charged. I would try not to worry, as it seems common enough. Cheers-Happy Holidays!!
 

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I noticed mine (only done just over 350 miles) was running at 15.3v. Whilst I did think "that's a bit high" So long as the car starts and there's no bells or buzzers going off, I'm not going to worry about it.
 

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I suspect this is why BMW and Mercedes provide so little instrumentation; nobody really knows what is correct and owners do not need to worry about it. I admit that I have been puzzled by the voltage read on my Porsche for the 6 months I have owned it. I am used to seeing the voltage regulator drop the voltage when the battery is fully charged, in my other cars. Because I do not drive enough to routinely fully charge the battery I could get an idea of when it was time to put the battery on a trickle charge. With the Porsche I used voltage in the 14's as a sign to do that. That worked well at first. But now that the weather is cold, voltage is routinely in the 14's and even just 15 on a battery that is fully charged. I guess I will not worry about it as long as the voltage is in the normal zone, but I will still try to use it as an indicator for time to hookup the CTEK.
Larry
 
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