96redLT4

I know this may be similar to several recent posts but I have always been confused by the matter. Car is a now 1 year old '16 GTS. Voltmeter reads 12.3 with the key on and the engine quiet. Charges to 12.4 and a green light on the CTEK tender after a few hours. Reading changes to about 14.5 consistently with the engine running. My question is, how do you know when there is a problem with the battery or the charging system? Can the voltmeter ever prevent you from 'becoming stranded'?? I know Porsche OEM batteries are notoriously crummy but have become better of late. I would like to think i can get 4 years out of mine.
Jim

Jabs1542

I always thought the volt meter in all cars was a warning device for the alternator. Voltage drops to zero, your alternator is not working (could be the alternator itsekf or a belt) and you are now warned to get this fixed immediately before your battery goes dead.

You can also use it to see how hard the alternator is charging the battery, thus showing signs of an aging battery.

In modern cars, including the 991, the volt meter shows battery status while the engine is not running, and the level of alternator charge when the engine is running.

96redLT4

My Porsche mechanic used to tell me to keep it on a tender b/c the tender is a lot less expensive than a Porsche alternator! I guess the resting charge of the battery is of little use as long as it holds that charge.
J

fast1

I agree that's its primary purpose, although an idiot light is better since it will more likely be noticed than a gauge.

GregD

I think when you pop the trunk open, you wake up the car, and whatever modules got turned on drain the battery slightly. I was seeing 12.19 on my car, and after I took the battery out of the car, it showed 12.51 !!! 0.3V drop seems consistent with my readings, so I'd guess your battery would be 12.6 out of the car, which is good. Besides it's a 2016.

That being said, since I put in my new battery my alternator's new consistet range is 13.5V, with only rare spikes in the 14+ zone. [EDIT - in normal mode] Prior to that, with the old porsche battery, it was 14.5-14.8 all the time... Just keep an eye on it. a 2016 Battery should be OK ! There's dates on the posts too.

[EDIT]: in sports mode , the voltage spikes +0.5 to +0.6V - you turn it on and watch it rise, turn it off and watch it go down... No idea what Porsche is doing and why sports mode would need more juice, but I'm really going to remove the Alternator display line and stop wondering about it now ;-)