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2012 Porsche 991.1 / ~68,500 miles/ Over-voltage issue – 15.3v at 2500rpm

Had a disturbing drive this morning – driving out to a Porsche shop in Ashburn to discuss some issues on my 1980 911SC – I noticed that the voltage gauge was climbing – past 13.5v…. past 14v.. up to 15.3v. NOT GOOD.

After discussions I drove back home – voltage stayed in the 15v range and I parked it. Started to troubleshoot the issue. Pulled up Pelican – then Rennlist – and all I could find are issues of undervoltage – nothing about overvoltage.

As noted car has ~68k on the clock and still has the original battery as far as I know = 8 years old. I am third owner – got it in Mar 2019.

Car starts just fine – but after a brief period – maybe couple of minutes voltage climbs from the 13v range – to 14v to 15v. I understand that it really should not go past ~14.7v in normal mode – [I don’t use sport mode that often].

I checked the battery with a multimeter after car had cooled down some – it was 12.45 at rest cranked it up and it went to 13.4 immediately and quickly rose to 14.7v within 2 minutes.

Battery is Duralast Platinum. No external signs of swelling or battery acid overflow.

?? Question: Is the voltage regulator for the 991.1 similar to that of the 996? 997? – where the voltage regulator is a separate sub-component? Or is it more integrated into the alternator?

I have no warning lights – just the reading of the voltage on the instruments.

What do you think?

thanks
kgl
 

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I'd say first of all is that you should get a new battery. Also, what was the OAT when you were driving? The 991 and 981 charging system will charge 'harder' or to a higher voltage in colder temps. Your battery is way past due to be replaced!
 

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outside air temp was in the high 40sF - I checke dthe battery this morn - and when cold it registered at 12.12v - which indicates battery is at 50% of its power. I'll do some more tests - but it looks like new battery time
 

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My '14 CS charges at approx. 14.9 to 15.0 at those temps . I am using a new 70AH lithium battery and the battery type has been coded as lithium during the install. I'm pretty sure your only issue is the need for a new battery. BTW, 12.12 v definitely indicates a week battery. You got very good service life at 8 years.
!
 

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I had a similar issue with my 2009 Boxster (base). I realize it is not the same vehicle.

At first, I was very concerned (freaked out?) about the high voltage.

When this occurred I found a few articles about "un-needed alternator replacement" and "porsche over charging alternator"... or similar.

I am not saying you should not replace your battery, I'm just sharing what I had found when this happened to me.

 
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