Porsche Battery Tender

[SignalY_GT3]

Have a battery tender from Porsche. It comes with a connector to the 12 V outlet but as many of you know (and it took me a few tries to figure this out because the Manual doesn't tell you), with the 992, the outlet shuts off 30 minutes after the car is off. So you have to have clamps and connect the tender directly to the battery. I did this and it works for several hours, it goes to full charge, then the on/off power lights start to blink, indicating an issue. The troubleshooting portion of the Manuel doesn't help. Any suggestions?

With my 992 I had no issue with the Porsche Charge-o-mat connected directly to the battery. Make sure you use the grounding point near the battery and not the negative post on the battery for your ground.

You can also try this procedure using the 12 volt outlet in the passenger footwell area:
PORSCHE 992
CHARGE-O-MAT PRO INSTRUCTIONS

1. Unlock Car
2. Plug Charger into Car Auxiliary Outlet
3. Turn Ignition Key to Accessory Position
4. Plug Charger into AC Wall Outlet
5. Select Charge “Mode”
6. Turn Ignition Key to Off
7. Lock Car

This works for me too.

[911-Purist]

When connecting directly to the battery, why connect the negative to a ground rather than direct to the battery?

Exactly the way I have done it on every car or motorcycle I have owned, even those with a battery sensor at the negative battery post.

My factory Banner AGM battery will be going into its 10th year this coming spring. And 10 years is a short life in my battery world.

[911-Purist]

When connecting directly to the battery, why connect the negative to a ground rather than direct to the battery?

Modern Porsches have an electronic module in series with the -ve battery lead integrated in the terminal connector.
This monitors charge and discharge current which is recorded in the cars battery monitoring memory and used for controlling alternator charging parameters.

If you connect a charger directly to the -ve terminal of the battery you are bypassing the monitoring system and potentially messing with the cars alternator charging settings.

Yes I came across that in a YouTube video. I am assuming it does that when the car is running.

The question I have is, when returning from a one-plus hour drive, I would assume the battery is fully charged at a 100% SOC when the vehicle is parked and shut down.

So now you have the battery very slowly discharging while parked over a longer period and since the ECU is not getting any power (and if it is, I'd like to see that stated in a Porsche document), how is the ECU recording a draw on the battery?

So by charging the battery while it is parked at the negative post to keep it at the 100% SOC as it was when the vehicle was parked and shut down, how would the ECU know any different? Just a thought.

Porsche likely uses the chassis bolt away from the battery for safety reasons.