Guys,
Open thread on the expectations of the Porche 991.2 auto battery charger. Not certain if the car is fully charging the battery.
My 2019 was just purchased from Porsche on CPO where a new battery was installed. But being careful, I also purchased a CTEK conditioner (shown below) to maintain the battery when the vehicle is not being regularly driven.

Today being beautiful here (78 degrees) I took the opportunity to drive with the top down for about 50 or so miles - maybe 1 1/2 hours of driving. The vehicle was reporting a charge voltage of 14.5. When I got home, I took the opportunity to change how the CTEK is connected - from using the 12V plug on the PASS side (PITA) to hooking to the battery + and ground. When I started the CTEK, the car voltage was about 12.4 which, for an AGM, means that that battery was about 1/2 charged.

After connecting the CTEK, it ran on a slow charge state (0.6A) in step 2 until the battery reached 12.6V when it shifted into bulk step 3. As for the other times I charged this way, the CTEK will charge all the way to step 7 and float (green) as expected.

So is the car's charging system not charging the battery to full health where a battery tender will? Brand new battery - I can't believe there might be something wrong with it but in any case, it fully charges with the CTEK.

I haven't had a situation where the car wouldn't start but I have seen it where it won't shut off at traffic lights when I'm in normal indicating a battery issue. Has any experience in this realm?

Update: got to float stage in about 2 hours at which time the battery reached 12.9V. so maybe I’m ok.

 

Unfortunately I don't have an answer for you, but I'm happy to pile on the subject. I've gotten to the point where my blood pressure rises any time I see anything on here about batteries...

After sifting through dozens of pages in multiple threads, I bought the Porsche-branded tender for way more than the equivalent part from CTEK because I wanted the process to be as simple as possible. Apparently the 12V plug in the passenger footwell is not only a pain in the ***, but won't accurately assess the battery's charge in my car; the display on the tender shows that there is no charge in the battery. Which is obviously not true because the car started immediately after with no hesitation.

I haven't reinvestigated since. Apparently now I should either try the plug in the center console (honestly can't recall if my car even has one), or buy the alligator clip adapter and hook directly to the battery.

What a pain in the ***. I've just tried to back the car out and drive it anytime the temps go above 40. That seemed to work for my Boxster last year.

 

I didn’t mean to raise your blood pressure. This is supposed to be a site where you relax. Sit in your beautiful car (love the color) with a glass of wine, turn on some music and don’t think about batteries!

 

Not so sure about this particular statement. There are 5 different conditions that must be met for the auto shutoff feature to activate. Battery condition is only one of them.

 

Ok now im curious... what are the others?

 

Probably:
Coolant temp
Oil temp
External temp
Electrical load
Air conditioning compressor on

In the winter the *** in my E63 never turns on. *** is also not active if water temp/oil temp are 'warm'. I can also turn off *** (have it start) by turning on the air conditioning. So those factors or some variation play a role in when *** is active.

Not sure about the Porsche as I always turn it off / run in Sport but suspect a similar algorithm exists.

Looking forward to what others actually know.

 

Now I can't stop thinking about spilling wine in my car...

 

Actually, just a couple. (Short quiz to follow).
Prerequisites for the automatic engine stop:

• Auto Start Stop function switched on
• Engine cover closed
• Driver detected: driver’s seat belt fastened and driver’s door closed
• PDK selector lever in position D, N or P or transmission range 1 or 2 selected manually or in the case of the manual transmission in neutral position and clutch pedal not depressed
• Engine, transmission and battery have reached operating temperature
• The vehicle has been driven at more than 1.2 mph (2 km/h) for at least 1.5 seconds since the last automatic engine stop
Exceptions:
The Auto Start Stop function is not available in the following situations,
for example:
• When Sport mode is activated.
• When PSM is switched off.
• During manoeuvring.
• When AC MAX mode is activated.
• When the “Windshield defrost” function is active.
• At elevations above approx. 9850 ft (3,000 meters).
• After engaging a gear without pressing the clutch pedal when the engine is automatically stopped.

The Auto Start Stop function is available with limited functionality in the following situations, for example:
• If the air conditioning or passenger compartment heating is operated at a high setting or if the defrost function is running for long periods of time.
• If the charge state of the battery is low.
• On uphill or downhill gradients.
• When vehicle-internal test processes are taking place, for example automatic engine diagnosis.
• In the case of excessively low exterior or battery temperature

 

[QUOTE=vanlieremead;17206869]Guys,
Open thread on the expectations of the Porche 991.2 auto battery charger. Not certain if the car is fully charging the battery.
My 2019 was just purchased from Porsche on CPO where a new battery was installed. But being careful, I also purchased a CTEK conditioner (shown below) to maintain the battery when the vehicle is not being regularly driven.

Today being beautiful here (78 degrees) I took the opportunity to drive with the top down for about 50 or so miles - maybe 1 1/2 hours of driving. The vehicle was reporting a charge voltage of 14.5. When I got home, I took the opportunity to change how the CTEK is connected - from using the 12V plug on the PASS side (PITA) to hooking to the battery + and ground. When I started the CTEK, the car voltage was about 12.4 which, for an AGM, means that that battery was about 1/2 charged.

After connecting the CTEK, it ran on a slow charge state (0.6A) in step 2 until the battery reached 12.6V when it shifted into bulk step 3. As for the other times I charged this way, the CTEK will charge all the way to step 7 and float (green) as expected.

So is the car's charging system not charging the battery to full health where a battery tender will? Brand new battery - I can't believe there might be something wrong with it but in any case, it fully charges with the CTEK.

I haven't had a situation where the car wouldn't start but I have seen it where it won't shut off at traffic lights when I'm in normal indicating a battery issue. Has any experience in this realm?

Update: got to float stage in about 2 hours at which time the battery reached 12.9V. so maybe I’m ok.




The situation you’re describing appears normal to me based on my experiences. I have noticed with my 911 the auto start/stop is more consistent in function after the car has had the battery tender connected for a few hours (e.g., over 24 to 72 hours) or after driving for a few miles (e.g., 50 miles). The latter situation is more variable relative to the tender. I’ve asked the local dealership/service department and was informed normal and my battery was in good condition.

 

John, if your voltage drops to 11-12v after a few days, why are you saying that it won’t start? 11-12v is still plenty of voltage

 

You are describing what sounds like normal operation to me?

The "On charge" voltage and "at rest" voltage are not the same. You are going to get different voltages with a meter across your battery, than you will when it's on charge. Your CTEK charger is capable of a fairly hefty amount of current (around 4.0 Amps) at charging voltage - 14 or more volts. (That's about the same value that your car's alternator was charging at, 14.5V, as you noted). 14 V from the CTEK is the "bulk" charge rate and sufficient to get fully discharged batteries up as rapidly as possible. It will (as you noted) switch modes and cycle the charging profile automatically. It should be (and usually is) set and forget device.

(One other note: "12" V batteries are typically composed of 6 cells, wired in series, each with a nominal full state of charge of 2.1V. So the nominal "full" condition, measured with a voltmeter, will be around 6*2.1 or 12.6V. At 12.4V, your battery was somewhere around 75% full (https://modernsurvivalblog.com/alter...f-charge-chart ). This applies both to traditional lead acid flooded wet-cell or more modern Absorbent Glass Mat batteries.)

FWIW I also use a direct connect pigtail on my battery, which on my '17 C2 is (I think) original to the car. It takes my 1A NOCO Genius charger about 8 hours to charge back to green if I've taken it for a drive. If I let it sit a few days, usually it's back to green overnight.


I think you are fine.

 

it is a strange system...what provokes madness in 991 owners is the voltage display. Too much information is provides and none of it is useful in determining the health of the battery.

 

Not necessarily. A “12V” battery is fully charged, settled, at 12.8V. It is 1/2 at 12.4V and essentially depleted at 12V (11.9). It may have enough strength to turn over a starter in a warm climate. I’d be concerned with a battery at anything less than 12v. It’s being damaged. As you said though I think I’m ok.

We’re traveling for a week. I decided not to put the battery on the minder, drove the car about 100 miles the two days before so the battery was charged. It will be interesting to see what the voltage will be when I get home. I’ll report back.