It's a gestalt, I tell ya! *NM*

After the installation of a Interstate H6 AGM battery--same capacity and type as the Banner OE it replaced --the car ran at 14.4V on the 20 mile trip back home.
Turned the car off and the battery read 12.5V on a multi-meter.
The next day, after driving it 10 minutes, the meter showed 14.4, then it started dropping and stayed at 12.5 but would occasionally shoot up to 13.9.
Same results the following day, except when I turned on sport mode, it immediately went up to 14.3.
The OE battery that was replaced was nearly 10 years old and mostly showed a range between 14 and 14.4v. I never got near 12.5.....
So, the question is this a normal display of a new fully charged battery with the alternator output being control by the ECM or something else?
Thanks for any help in advance..

Because it's a new battery, the ECU can finesse the charge for optimum maintenance.
As the battery gets older it isn't as "flexible" with low voltage and requires higher voltages to maintain its charge.
All perfectly normal.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

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Thanks Pedro.

Fully warmed engine (if that makes a difference) the dash display read 14.5 with no difference in Sport or Normal, nor AC on or off. Saw 14.4 for a split second when the top closed.
I've kept the car on a plain Die Hard maintainer for most of the life of the car if it sits for more than a day.
Initial cold reading with engine off is about 12.3 (no maintainer) to 12.5 with. Starter engagement drops it to high elevens, but it recovers immediately.

Btw, it's my understanding that the regenerative system doesn't function if Auto Stop/Start is disabled.
And about that, when I've (rarely ) bungled a takeoff, the engine may stall for a split second, but immediately restarts. I suppose that's an "always on" feature.

Key on reading about 13.5.
Engine on dipped to 12.7.
Idling (not cold rpms) 13.5 to 13.8.

Laz--What procedure do you use to get the dash display to show voltage?
Jerry--2016 981S

• With at least ignition on, or engine running, push the lower right wand (the cruise control) forward.

• Select Settings

• Select Display

• Select Vehicle Menu

• You should then see the currently displayed parameters, and you can have up to 4. By selecting any of the 4, you can then select (from several choices) what will display.

• Pulling back the wand will bring you back through the menus to the actual display.

(My selections are coolant temp; oil temp; oil pressure; voltage.)



Edited 1 time(s). Last edit at 09/12/2022 11:30PM by Laz. (view changes)

Hey Laz, you have your display setup just like mine. Taken a couple of years ago with cold engine on a warm summer day. Always kind of interesting that the coolant and oil temperatures are usually a bit different when the engine is cold. You'd think that in the garage, they'd be the same temperature.



Is your cruise control and display control on the same stalk? On my 2014, the cruise control is on the bottom left. Display control stalk on the bottom right.

[www.britannica.com]



Edited 2 time(s). Last edit at 09/14/2022 10:42PM by Laz. (view changes)

I'm not sure where the coolant temperature sensor is located. My guess is it's near the thermostat in the engine. The oil temperature sensor is probably part of the oil level sensor located in the oil pan under the engine where it will be influence by ambient temperature more quickly. So in the pic that I posted, it could be the dropping overnight temperature has cooled the oil closer to the ambient temperature and takes longer to influence the internal engine temperature. Also, the fact that heat rises would suggest that the top of the engine would be warmer than the lower (lowest) part where the oil pan is located.

On the other hand, it could just be two slightly differently calibrated sensors.

Laz--Thanks, my fourth setting was blank, but is now set to voltage, the same as yours.

Quote
Laz
Fully warmed engine (if that makes a difference) the dash display read 14.5 with no difference in Sport or Normal, nor AC on or off. Saw 14.4 for a split second when the top closed.
I've kept the car on a plain Die Hard maintainer for most of the life of the car if it sits for more than a day.
Initial cold reading with engine off is about 12.3 (no maintainer) to 12.5 with. Starter engagement drops it to high elevens, but it recovers immediately.
.

It's interesting how the reading differ. My 981 S is now a bit over 9 years old and on the original battery. I also use a maintainer if the car is going to be sitting for much more than 4 - 5 days. The readings can vary while driving at steady cruising speeds. Generally, the reading will be between 13.5 and 13.9 V. Sometimes, mainly when temperatures get cool in Spring and Fall, the readings will get up around 14.4 and occasionally higher, even with the engine warmed up

With mine, once the engine is warmed up, in Sport Mode the readings will go up from the mid 13's to the mid 14's. Turn Sport mode off and the readings will drop back into the mid 13's

Edited 1 time(s). Last edit at 09/13/2022 09:29AM by Laz. (view changes)

For an AGM battery, 12.5 is low and more like above 12.8 to 13.0 is fully charged. Are you running the tests with the engine and alternator running? After how long after shutdown? How long was your run before parking the car to give the charging time to recover the change used in the start?

Original in my 13 Boxster S, delivered June of 2012. As mentioned before, it's kept on a maintainer when not used for more than a day or so. At first I used the dealer's complimentary Charge-O-Mat, and when that went kaput a couple years ago, a simple Die Hard. It still goes to float charge as always, but lately the cluster Volt reading just before cranking, is often in the high elevens rather than the low to mid twelves. I checked the maintainer's float Voltage and it was in the mid-14s, which seems high for that circumstance. When the engine's running, the cluster Voltage ramps quickly up to the 14s; a couple days ago observing 14.8 momentarily, but staying in the mid to high 14s. Sometimes it drops back to the mid 13s, which seemed fairly normal over the years. In its early life, I once observed 15 something while going down a miles long fairly straight highway. (I've read the regenerative braking is disabled when the Auto Stop/Start is, too. I never use it.)
Maybe, maybe, I felt a split second delay in cranking once last week.
Don't wanna find out on a freezing day (coming soon!) that the batttery's dead as the proverbial doornail.