cmorales954

...I just bought another can of the stuff!... so I guess I'll be able to put it to good use if I can access it. Looks a bit buried but maybe not horrible?

Rich_Jenkins

Back to the battery for just a second, a zero-cost check on condition (I know, your guy said it was ok, but still) is to observe the start up voltage when the key is first turned on overnight? You'll need to add Battery Voltage to the Multi-function display.

I can say that my OEM Banner 80 Ah (prod: 04/17) was giving me 11.4-11.6V after four years service when I checked it a few months ago. I decided to replace it with a 92Ah Duracell from Batteries Plus, and now I routinely see 12.2-12.4V just before hitting "start".

Just something else that you can check/confirm/eliminate. I do find German cars in particular seem afflicted with weird electrical gremlins when the service battery is on its way out, and while I'm not sure it's the case here, it is an easy data point to obtain while thinking of what to do next.

cmorales954

I've got a full load-based tester I can bring over to try, as well -- thank you for the suggestion! I want to say my charges have looked healthy, however. I have a boat as well and monitoring battery performance is even MORE important (I learned the hard way on my first boat, with a dead battery when 7 miles offshore!), so I am used to wiring those up and keeping tabs on their health.

fpb111

Hook up a battery maintainer for the next week or so.

cmorales954

Getting 12.2v before cranking, but after it has sat for ~6-8 hours, so I just don't think its the battery.

Chimcu

Isn't opening our frunk at night is a good thing.. lol

Greg D.

I know that before cranking, some computers have already fired up and depleted the charge, but 12.2 isn't as fantastic as you think.
The one time my battery took a dump, the frunk and the driver door unlocked themselves too! I thought that was a safety feature, maybe it's just luck.
Is it unzipping its fly when you are driving and the alternator is giving you 14V ? I bet not. It does it at night at lowest voltage.

I *just* measured my battery voltage at the connector I installed outside the frunk to recharge it easily (just for you, and it's chilly outside, nipples poking thru my shirt, please appreciate the effort) -> 13.2V (antigravity)....

So I *still* think it's your battery. I know you said yours was tested, but how? mine was tested twice also: it showed good on an old tech tester, but once I took it out of the car and it was disconnected, a "solar" brand quality tester that measures CCA showed it has lost 250 CCA of its origical 800CCA and returned a "bad" state despite more or less OK voltage. All this to say there are testers, and then there are better testers... And low voltage did the same to me. Maybe, before you spend your life chasing wiring issues, you do try a *new & fully charged* battery that can be returned? if it pops on THAT then you know for sure. If not you'll need a battery soon enough anyway. Basic troubleshooting, start with the simple stuff. Still putting my $ on battery, the 991 is a battery hog and does strange stuff on lower charges.

PS; Another possible test for ya: connect pigtails to your battery that stick out of the frunk by the windshield (good for plugging in to a maintainer). Plug it to a maintainer overnight. See if it popped in the AM (bet it does not). You do have a battery maintainer right ?

cmorales954

haha... thank you for braving the cold

I live in a warm environment (mid florida, with mornings already in the 70s) so that should be considered as well.

The car is scheduled to go back to the shop next Wednesday for minor items. I can ask them to double check the health. Ill also try on my own tester this weekend.

ChrisW991.1S

So mine did this to me recently under different conditions (when coming to a stop while driving) but it ended up being the key fob battery. I'd go ahead and replace the fob battery if you haven't already. Weird... I know!

Rich_Jenkins

I like this idea.

Another option: If you have a can of compressed air, and you can locate the FECU, take the can and shoot it for 20-30s at the FECU. The air will get extremely cool by that point. The thing is, any semi-conductor array in the electronics of the FECU, which is sketchy due to temperature (as in, overnight?) might be affected by the cooling. This is just another trial thing you can do; besides whacking things with a mallet, was part of the usual approach for trying to work out why certain of the components in my cabinets (long story, I'm out of the Aerospace biz) did/did not work.

If the FECU trips the frunk while it's cooled this way, chances are you've confirmed it as the issue.

cmorales954

Literally first thing I did when I got it was swap the FOB batteries so we should be good there.


I'll try that tonight; I have an AGM-approved battery maintainer. When driving the voltage shows 14.6. I briefly checked the outside of the existing battery and couldnt find a date on it. I'll check closer this weekend. I also checked the system with an icarsoft and couldnt find previous battery details.

Rich_Jenkins

FWIW, on my 17 C2, the OEM Banner 80 Ah battery installed by the factory was stamped with the month (14) over the year (17) of production in one of the terminals; this is what it looked like:

cmorales954

Mine isn't the OEM battery; it got replaced at some point by AAA with the original owner. It's an AGM and 'only' 70ah. Need to dig around more cause there was no obvious stamp/sticker when I took a photo of the top of it.

DaveGee

It was recently pointed out to me that the stamping on the battery post is the week and year of manufacture, not the month and year. Otherwise, my battery was manufactured after I took delivery of my car.

Agree with Rich on all other points. I too suspect the battery.

DaveGee

cmorales954

Took a multimeter directly to the battery this evening after the car sat for about 1.5hrs; coming in at 12.55. Put a battery tender on it anyways and will see what it reads in the morning.