limegreen

With the end to the mild winter that wouldn’t end now approaching I needed to take my car out of its 3+ month hibernation last week.

The car has been on a Porsche maintainer all winter connected to the 12v outlet in the passenger foot well. It initially started up with no trouble but now has a strange issue.

I’m used to seeing the battery voltage climb to 13-14+ V immediately after startup but now even after idling for 10 minutes it still remains at approx.12.5 V and will only climb to a more normal range of 13.5 + V once it’s revved to over 3k rpm only to drop as the engine falls to idle.

There are no load consumers on ( headlights , rear defrost , etc.).

See video :

I haven’t driven the car on the road yet and have only moved it around in the garage / driveway .

Has anyone else experienced this before ? Not sure if it’s an alternator issue or somthing related to a module / intelligent electrical system etc .

Please advise...
Thank you !

CSK 911 C4S

I think you're good.

The battery is probably just topped out.

Drive it around a bit and report back.

LexVan

What year is your car (how old is battery)?
Why are you just letting it idle for 10 minuets?

limegreen

The car is a 2015 ( Late 14 production).

LexVan

Thanks. Battery should be fine, then. Think about battery replacement in late 2019. There is a GREAT battery DIY theard here in RL.

limegreen

Is this situation that I'm seeing something others have experienced? My experience has always been that once an engine is running the vehicle electrical system operates well above resting battery voltage under almost any condition.

abe

That is my experience too ...usually stays around 14.6 on Sport Mode with very little fluctuation.
Abe

cyberay

For the past few years manufacturers have been tapering the charge voltage as the battery approaches full charge condition as a fuel saving effort. If you could monitor charging current you'd most likely see it go negative at the same time because the battery is in a full charge state, just like yours is now after sitting on a tender for 3 months. After a couple of starts it will sense the need to charge the battery and the voltage reading will return to what your used to seeing.

sdl2112

Try sport, sport+ mode. I believe it bypasses the fuel economy mode of charging only under certain conditions.

Pavegeno928

SPORT/SPORT PLUS it runs about 1.5-2 volts higher. Normal mode around 12.5-13 volts.

limegreen

Gonzalo38

After doing a lot of reading about batteries in the 911's, I decided to buy a battery charger last week. I decided not to buy the Porsche charger because of its high price in my country, and went with an Optimate 6 instead.

My 991.2 Cab was delivered new on January 2018 and it was normal for me to always see the voltage indicator at 14.8 V. On very few opportunities I would see it around 14.0 V.

When I connected the Optimate charger, it almost immediately went to the "Save Battery" mode, which indicated that the battery had low voltage. After almost half a day of charging, the charger showed that the battery was ready but I decided to keep it connected for maintenance until to day in the morning.

Today the car started without problems (as usual....) but I was surprised to see that the car voltage indicator was showing 12.2 V during most of my drive (with few opportunities going up to 13.3 V). Only when I connected the rear defroster the voltage would go up to 14.8 V. Is it normal to see such low voltage ? I guess that this is a good indication that the battery is in good shape and fully charged ?

By the way...... I'm planning to leave the charging cable permanently installed. Has anybody done this ? Is there any suggested place near the positive side of the battery were I can install the negative cable ? Right now, the place for the negative cable is on the opposite side and I just want a closer place since my cable is not that long. Any suggestions were to hook the negative cable would be appreciated (with pictures if possible).

limegreen

I have yet to drive my car as the winter weather has refused to subside. I have started the car and moved it around several times in the last 2 weeks and after the 4 or 5th start I noticed the charging voltage back up around 14.5 - 15V all of the time per usual.
I have the car again on the charger so I expect to see it producing those low voltage readings the next time its run.... It's very odd, but then again it's the only newer car that I own with a voltmeter.

trevorlj

I just installed an Odyssey PC1350 a couple weeks ago:
https://shop.odysseybattery.com/p/pc1350

...60 lb monster with 195 minutes reserve capacity. With it fresh off the charger my car shows ~12.5V for extended time while cruising. Once I drive it for a few days it spends less and less time under 13.0V. I'm pretty sure that's by design to save gas as cyberay mentioned. You would be surprised with how much torque it takes to spin a loaded up alternator.

Gonzalo38