CaptainL

Almost exactly 1 year ago I took my 2017 991.2 to a local German car shop to preemptively get a new battery installed (daily driver). A couple days ago, it started really slow. Drove it around for 45 minutes and then it started fine. Sat for 36 hours and barely started this evening. So I drove it around again for a while hoping it will charge enough to start in the morning so I can get it back to the shop(was showing 14.8V). I take a look at the battery tonight and it is a non AGM battery that specifically says not to be installed in AGM cars. I'm assuming that is why the early failure. So I will go tomorrow morning and have them swap it out.....If it starts.

If its dead, can I go get the appropriate battery and just swap it out myself. I do NOT have a trickle charger as I don't need one usually. I've read on here people just swapping them out and then some talk about reprogramming the PCM???....which I don't think I can do.

I'm kind of disappointed the shop messed this up as they are close and have been doing my oil changes/brake flushes.

Thoughts?

Thanks!

Porsche_nuts

Yes you can swap to AGM battery yourself. Done like any other battery and there is a thread here somewhere and YT vids as well.

No need to program the battery, although others have. If you do not, nothing bad will happen.

Do not know how your shop can make such a mistake.

CaptainL

Prefect. Thanks.

fpb111

You don’t have to register the battery swap. However if AGM was selected at the last change, ether by omission (just didn’t change program parameters or .?) and a flooded Battery was installed the flooded battery could by cooked dry suffering early death due to higher charge rate required by AGM.
i just went through this following this video.

IXLR8

Pretty scary when an owner knows more about something like batteries and charging systems than any shop does. Different battery chemistries such as a GEL, Flooded Lead Acid or an AGM each have different charge algorithms. Taking a car to a shop is like letting the fox loose in the henhouse.

Porsche_nuts

yeah, if they can't get a simple battery change done, who knows if they ever got the oil and brake flushes done right.

Bud Taylor

Would be marked off my list. Some shops are good with old cars but suck with new ones and vice versa. This may be the case with them. Im supprised it worked that long and good news is if it wàs gonne fry something it probably already would have happened.

CaptainL

Yep. They definitely are not doing my spark plugs or PDK service next year.

CaptainL

So, the shop it closed until Monday of course. Any problems if I disconnect the battery for the weekend so it will hopefully have enough charge left to start Monday? Thanks.

asellus

you'll need to reindex the windows and seats, but otherwise no issues.

if disconnecting the battery is what allows it to have enough charge then the battery is probably not the problem. FLA batteries don't self-dischargethat quickly.

CaptainL

Yeah. I was trying to figure out alternator, starter, or battery. It starts up fine after driving for 30+ minutes. But struggles when it sits overnight or longer. When I saw they installed a wet battery I assumed that was the problem....but maybe not? I'm headed out of town this weekend so I don't want to risk it not starting when I get back. Guess I don't have many choices right now. Any other troubleshooting ideas I can do today?

IXLR8

In your initial post, you did say 14.8V which tells me it is charging. Chances are it is not the starter. Why not fully charge the battery off the vehicle and do a battery test on it. It'll give you an excuse to buy some test equipment. Do the easiest and cheapest test first. Do you have a battery charger, a DMM and a load tester...?

CaptainL

That's what I was thinking. charging at 14.7 this morning. I should have just done the battery replacement myself initially but was busy at the time. I don't have a charger or anything. I'll probably just take it in Monday. Just a pain to wait over something so simple.

SilverSFR

Everyone should own a battery charger. Buy yourself a present for the holidays.

Joec500

Had the same issue except is my fault. I just defaulted to the battery in the battery finder for the manufacturer and ordered a battery based off their Part number. 1.5 years later it died. I replaced with a generic AGM from pepboys and fast forward 3.5 years and it works great.