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Just had to have the battery replaced car has 4000 miles on it. I still think there’s something going on with the charging system only runs @12.2V ?the dealer ran the test they said it was OK. He said the Charging system is designed run at 12.2 V to Save gas.Seems really low to me when I first start it’ll go to 13.3 and when I decelerate it’ll will show higher .But general driving it’s only running 12.2. normal?What is yours? Thanks carl
That's how AGM charging systems work, there isn't 13.3V across the battery all the time as the alternator is only engaged when the battery needs a boost - it improves MPG. If the battery doesn't go dead in a couple of weeks, you'll know its working, or not. That's why when you first start it, the battery is "weak" from turning over and it goes to 13.3 instantly.
That's how AGM charging systems work, there isn't 13.3V across the battery all the time as the alternator is only engaged when the battery needs a boost - it improves MPG. If the battery doesn't go dead in a couple of weeks, you'll know its working, or not. That's why when you first start it, the battery is "weak" from turning over and it goes to 13.3 instantly.
Mine runs at 12.2 when it's fully charged. When it's not, the charge will remain at 13.x or 14.x until charged. I leave Auto Start/Stop on most of the time so I see it recharge more ofter.
Funny I’ve had two GT4s both charged 13.5–14.9 never saw anything under 13. Just seems to me that letting a battery run less than fully charged is a recipe for problems. My battery got replaced today 4000 miles less than a year ,was it a bad battery? Or was it caused by being under charged? I get the idea for better fuel economy by having less Drag from the alternator but 12.2 Could be just too low? Carl
Runs around 12.2 to 12.8. I stopped looking at it as it varies wildly.
same deal drives me nuts looking at it 12.2–12.8 . So paranoid,I actually bought a jump starter that I put in the car just in case the battery died . The one that got replaced failed several times .i got done from a drive and the battery was so dead it wouldn’t turn the car over. Probably a combination of a bad battery which was replaced today and being chronically under charged ,which probably exaggerated the weak battery. At least that’s my theory? Carl
The first thing I'd do is to put a Digital Volt Meter across the battery with the engine running at ~2,000 rpm. A cheap Harbor Freight Digital Voltmeter is good enough for this situation. Now, compare that Digital Volt Meter reading to what the dash gauge is showing. We start here to even see if there is a true electrical charging system problem or a gauge problem. It is possible that the dash gauge could be inaccurate and/or it's connections to the electrical system of the car are compromised in some way. One or two tenths of a volt difference between the two would not get me worried. However, the normal charging system voltage of a 12.8 volt lithium battery, which is what your Porsche has (if it has the Li battery), is around 13.4 volts. FWIW, 12.2 volts is absolutely not correct. If that's what you're reading across the battery with the engine running at ~2,000 rpm there is either a charging system problem or a wiring problem somewhere between the battery and the alternator. If you do NOT have a Li battery and the battery you have is an AGM or Flooded Lead/Acid battery, the charging system voltage at ~2,000 rpm should be ~14.0 volts +/- 0.5 volts.
Last edited by Bluehighways; 02-19-2022 at 03:03 AM.
I have an AGM battery and the normal output (in normal mode with Auto Start/Stop activated) for the alternator is 12.2V when the battery is fully charged. It will deviate from that when braking or when it needs to charge.
EDIT: The above is relevant while driving in the city. I haven't followed battery gauge too closely on highway driving.
I haven’t drive my car often (once every couple weeks), my 22 C4S with AGM battery was showing 13.4v on the PCM display for my hour long round trip yesterday. I also drive in Sport Mode FWIW.
My 991.1 has a similar voltage gauge compared to your 992.
Mine shows 12.1 V (original picture from my dash) Battery is at least 5 years old if not older and still going strong.
As far as I understand the gauge, there is an operating range/voltage which is ok for Porsche means and that is between the two pink bars. (drawn the bars to visualise the range).
Sure I don't know the number where the left/minimum/red bar starts, but I guess/assume my 991 will tell me when its too low!?
I might be wrong…any insights? Thank you!
02-17-2022, 03:21 PM
Dealer says 12. 2 V is correct? What is yours?
