That is completely contrary to everything i have ever heard or experienced. It truly sounds like the shocking reversals in other previously-unquestionable ideas going on throughout the world today, like weight loss, diarrhea, the "benefits" of alcohol, the benefits of communism, etc.
I will not ask if you are sure, because it appears you are sure.
However, id like to hear from others, because my own experience is contrary to what you say. I have started a car with a very weak batt that barely turned the engine over, then driven or revved for a while, and then stopped and started the engine and the battery was back.

If what you say is true, then the car batteries are on a progressively and accelerated dying path everytime we drive the cars.
It also points to the NECESSITY of putting batteries on a tender/recharger after being driven, right?

Yes you can recharge the battery a little if you drive the car for like 20-30 miles, will it be fully recharge if it was almost dead, probably not. I have an older car that I almost never drive, and I do start the car every 3 weeks or so and let it idle for like 90 minutes. That gives it enough juice to start again next time. But if I don't start the car for 4 weeks, it will not start.

I can also give you another example. My wife's Lexus es300. She only drives the car to and from work a couple time a week and a couple of stores here and there plus the kids to school (very close to home) . Her job is 3 miles down the road.
She usually kills the battery within a year or two at most, as the battery doesn't really have time to recharge enough during her driving. Yes, the car usually starts without any issues as the short drives may recharge it just a little, just enough to start again, but after a year or most two it's almost dead and needs replacing.

This is from 'Optima Batteries' the manufacturer:

"Look at the first installation instruction on this alternator box, which is printed in bold text, for additional emphasis- "CHARGE BATTERY - (12.6 Volts min) The alternator isn't designed to charge a dead battery. Premature alternator failure can occur and may Void Your Warranty. Alternator manufacturers know the same things about alternators that we do- they are designed to maintain batteries that are near a full state of charge, not recharge deeply-discharged batteries. We post this on message boards and in groups all the time, but there are still folks who are convinced their alternators are designed to recharge deeply-discharged batteries. We know this, because they call our tech support lines on a regular basis, because their battery keeps getting deeply-discharged (it is actually just staying deeply-discharged). The alternator manufacturers also get calls from these folks, because they've burned up their alternators, trying to recharge deeply-discharged batteries."


From Autozone:

"If you have a dead battery, jumper cables can be a real lifesaver. And while boosting the battery to get your car running can get you on your way, you shouldn’t rely on running your car to recharge the battery. It places enormous strain on your battery and the alternator and can contribute to premature failure in either or both.

When you jump-start the engine, you’ll often hear a loud whining noise from the alternator, albeit temporarily. That’s because it’s being forced to work at 100% for a long period of time where it’s only meant to produce that kind of effort in short stints. It generates a lot of heat both at the alternator and at the battery.

This amount of stress can cause the voltage regulator or rectifier diodes to fail, diminishing the charging output from the alternator. In the battery, sulfation can occur that essentially short-circuits plates inside after some time, leading to premature failure.

If you have a dead battery, it’s always best to recharge it slowly with a plug-in battery charger."

Yes, I am absolutely sure. You were wondering why you car was taking 1-2 hours to reach full charge after driving the car, and I told you why that was normal. Driving a car does NOT fully charge a battery because that's not what the alternator is there for.

It assumes the battery is charged properly to start with, and is there to maintain that capacity under load, not to put back a charge that should have already been there in the first place, and you can have all sorts of gremlins on modern cars if trying to do so. When you put any load on a battery, the voltage sags under that load. The alternator is there to help keep the voltage stable and helps the battery maintain those loads.

A low battery needs to be fully charged on a proper battery charger. As I stated previously, this is a very common misconception for many despite always being this way. And yes, this is precisely why those that routinely use a tender can get many more years of use out of a battery than one that sits without one, as it keeps the voltage where its supposed to be and slows the sulfation process which occurs when the voltage is lower than its supposed to be

Idling, even for 90 minutes(!), is not effective at establishing and maintaining a healthy charge. It may 'work' but it's not good for the battery or the engine or anything else. Put a maintainer on the battery and stop firing the car up if you don't intend to drive it.

I know that, but where the car sits, I can't do anything else with it. I have been doing this for a few years without any problems. The car has 300k and I don't really care if anything happens to it anyway.

DaveGee

Yup I got a Duracell for my Cayman from Batteries Plus and a NAPA AGM for the 87.
Both are East Penn.

The collective drivers-seat research continues...

I tried to trigger Auto Start Stop in my 981 but was UNSUCCESSFUL. Auto Start Stop is not working in my 981 with an un-coded battery.


Auto Start Stop
The Auto Start Stop feature is the reason for the need to code the battery in the BMS (Battery Management System). For all cars with Auto Start Stop, not just Porsche.
There are other names/acronyms for the BMS but none of them are referenced in the Cayman Service Manual (but obviously a Management System exists in our 981's).

Auto Start Stop puts a much more persistent/greater load on the battery and therefore requires more charging for the battery to be properly maintained.
So if Auto Start Stop is not being used there is less load on the entire system. If the battery is not coded in the BMS, Auto Start Stop is disabled.

So one question is: How did the BMS learn the battery had been changed? (via the wire that was cut in the video above?)


The Alternator
Fun fact - the Cayman Service Manual only references a Generator (at least in my version of the manual). But our 981's are definitely equipped with an Alternator.
The output from the Alternator typically ranges between 13.5 and 15 volts and it can be affected by engine speed, temperature, and load.
In our 981's, the output from the Alternator is massaged by at least two different Transformers, which can step the voltage up or down (depending on the circuit being fed).

In my 981 the voltage reported from the Alternator (assuming its pre-Transformer and not post-Transformer) ..is 14.7v and the voltage reported at the battery is 13+v (likely ~13.8v)
I think my test results indicate the the battery charging circuit controller works to maintain ~13.8v stepping up or down as needed to feed the battery.


So longer story shorter,

• If you're using Auto Start Stop then definitely code the battery in the BMS.
• If you're NOT using Auto Start Stop then don't worry too much about coding the battery, but definitely use a battery tender/conditioner.

Not sure if that 100% true that you need to code the battery for stat/stop to work. On my original 10 year old Porsche battery which still worked great, the start/stop did NOT work anymore. When I replaced the battery with a non-porsche battery and did not code the start/stop started working again.

I had the same experience as Tomekz with the start/stop working again after the new battery was installed without the coding. I think that is based more on voltage available on the battery.

I installed a Lithium Ion battery 4 years ago, and the start/stop works fine, no recoding.

I agree.. Apologies for any confusion.
At a stop light yesterday, gave Auto Start Stop another chance and suddenly the engine shut off!

I think what many people are missing is that it's likely the charging system compensates for the battery age, for even if the new battery is the exact same rating, it doesn't have the same electrical characteristics. So the software needs to know when the battery has been replaced. Coming from a battery charging and gauging background, I know that the algorithms often have models of the battery characteristics so they can predict state of charge accurately to control charging. I can tell you from experience this is really tricky stuff. The software has to opportunistically glean hints about the battery condition based on the normal fluctuations of voltage and current - it has no direct information. Thus it likely uses the age of the battery as one of the inputs to the model.

Rehashing this old thread rather than making a new one.
I had my 2014 Boxster in storage on a maintainer and I think it destroyed my battery.
After taking hit out of hibernation, I noticed that the battery would drain super-fast when the car was in ACC mode. Like, it would go from 14ish volts down to less than 12 in a minute or so, giving the shutting of the outlets and eventually completely shutting down the system messages.
Strangely, I could start the car with no sign of struggle on the starter. The voltage would fly right up to 14 then keep climbing up past 15V. I turn off the engine and watch the voltage fall back down under 12 volts in a matter of a minute, then start it right back up and rinse and repeat. Once again, no sign of struggle on the battery.
I bought a battery tester and it did say replace. So I took a look at the battery and was surprised to see that it was stamped form 2013! Holy cow. Almost 12 years of service out it.
Anyway, my issue is that the new Walmart (East Penn) H7 battery I installed is giving me the same super-high charging voltage. 15.4 V! I did code it with the proper Type and CCA (800) with an iCarSoft POR 2.0, but the high charge voltage did not go away. I drove it for 20 minutes and saw no change in voltage whatsoever.
Based on @DaveGee 's post showing charge and float voltages, it seems that this is still in the realm of normal behavior? The battery was fresh with a 3/25 sticker so it seems add that it would need such a large max charge. Battery tester showed it to be good, with over 800 CCAs actually. On a positive note, it does hold a charge of mid 12 volts for a very long time in ACC mode, so I am confident the battery is good.
Should I be concerned?
Any possibility of damage to my charging system with the maintainer? It was a generic GOOLOO S10 6A charger maintainer off of Amazon.