Apothecarian

Hello All

What is normal start up reading ? I have 2013 base Carerra. Mine rewards 14.2 a 14.4. Thank you.

GregD

That must be with the engine running and the alternator charging (or immediately after shutting it down, since your other readings indicate a hot engine )... If you want a true reading of your battery check the reading first thing in the AM with the ignition on but no engine. A normal battery reading is 12.6V. anything less than that is no "bueno"....At 12V a battery is essentially dead for example.
Your 14.3v suggests the alternator doing its job of charging it, and it generally reads higher when in sports mode (why? no idea but it does jump up in sports mode).

pfan

My 2013 S shows 12.1v with the key on prior to engine start. While driving in normal mode, the display initially indicates 14.5v. After approx. 30 minutes of driving, the display will usually drop down to 12.8 or so.

The odd thing is that my battery load tester tells me the battery is just fine. It's fairly obvious the battery is showing it's age, but I guess I'll stick with it as long as the load tester readings are ok.

Sidvicious7

Your battery is fine. I concur with the previous post: "A normal battery reading s/b reading 12.6 VDC."
A reading of 12.8 VDC indictates a good battery.

Double_J

You're fine. Mine shows at 14 and change at startup, high twelves while driving.

pfan

I see where some owners have elected to replace the battery as a precaution, but are there any reports of battery failures yet on the 991?

GregD

We've sorta circled the wagon on this on another thread but it's tricky....

A battery at 12.1 V is emphatically *not* fine... A quick google search will tell you that a 12.1V battery is holding about a 50% charge only. Now the problem here is can we trust that reading? By the time you either a) open your trunk to check or b) get in the car to check the display, you have "awoken" the car and it's probably lowering your reading by 0.3 V already because it's powered up some modules. If you had direct wires to the battery you could check or could access the cigarette lighter for a reading without opening a door, then OK, it would be a valid reading of 12.1.. More likely you're at 12.4.

So for me (and only me), the reasoning was: I do not like the odds of a 4y/5y old battery reading 12.1 in the AM combined with my alternator putting out 14.5V to 15.2V regularly... Seemed high, and a replacement alternator is probably $$$. I bought a new battery and immediately thereafter (and henceforth) my gauge readings have been better - the car lives between 13V and 13.8V now - i.e. my alternator is not working *quite* as hard...

Oddly, my old battery once out of the car read "normal" as well per the tester, yet the new one really made a difference in my daily readings.... YMMV, you decide what your reality is, with no judgement from me ;-) I noticed a difference though, both in alt output and cranking speed...
The only time I see 14.x now is in "sport mode"...

digits

Mine gradually drops down to 12.4 with the engine off as measured via vehicle info. Yesterday I had my oil changed by the dealer and the accompanying inspection report showed that they measured 12.6 and labeled that as "good". I wonder if they measure at the battery - or if they actually measure at all. If I remember, I might go stick a volt meter on the battery terminal and see how closely it matches the info display. The battery is at least 1 year old.

CDH911C2S

I replaced mine @ 4 months ago as some electronic gremlins started to appear....all gremlins disappeared when I replaced the battery. The entry /exit lighting system stopped working---although the car started quickly each time---and was driven in excess of 5,000 per year.

GSIRM3

As you have stated in two posts above, for some reason, voltage reading is definitely higher in sport mode. I can be driving in normal mode at somewhere between 12.6 and 13, and as soon as I engage sport mode, mine will increase to 14.4-14.7. I keep my car connected to a CTEK maintainer when in the garage and not being driven. My voltage readings have consistently been as stated above since I bought the car new, one day after arrival at the dealer. It is now 29 months old.

LexVan

Mine failed, and was easily replaced under warranty in 2015. Wouldn't hold a charge.

Oh1-911

My charging voltage is about 1.2 volts higher when in sport mode, and others here have mentioned this. Question is: Why? I don't know of any higher electrical load when in sport mode. Does Porsche think that the radiator fans are going to run more often?

CSK 911 C4S

^^^^ this caught me totally off guard the other day. Thought my car was wasn't charging properly. I usually push the sport button right as I start up.... but the other day I drove a piece in normal mode and looked down and it was reading 13.2v when I'm used to seeking 14.4v...... freaked me out for a few minutes..... even had the the battery and alternator tested later in the day..... all was good.

Oh1-911

Any ideas out there or info/links you guys have found that explain why the charging voltage goes up roughly 1.2 volts when in sport mode?

Mike Murphy

Super interested to find out why this would be the case. The only speculative thing I could possibly think of is that engine RPMs are kept higher and therefore, the alternator is always able to hold the voltage. Or that the regulator allows for higher voltage for better spark wattage (although this is mostly an old-school trick that probably doesn't apply).