IchBautAuto

Back again with more questions. I have read up all the relevant articles thrown up by search and haven't been able to see a definitive result. Both specialist indy and dealer mechanics are quoted with differing outcomes.
I should add that I have a data logging device fitted and an in-cabin readout to keep me on top of the actuals. The car itself is or seems to be running perfectly, getting consistent fuel consumption and so on.
So, my problem. I am on a 2000 Km trip which is following a 1200 Km trip last month. Starting has been faultless ever since I religiously put the car on a trickle charger if not driven for more than 4 days with a lot of local stop start driving in the mix.
I start the car and travel in roughly 300 Km stages so there is some consistency. At highway speed unless stops for roadwork or passing through a town.

The most common situation is Voltage gets to mid 13's on first start and sits there with the car running around 2000 RPM for the entire stage. Stop the car for a fuel stop etc and on re-starting the charging voltage goes up the 14.4 and stays there for the 300 Km stage and the same again for the rest of the days driving stages.

A less common situation is the car starts with 14.4 V and mid stage if you slow for a town or roadwork, doesn't regain 14.4V. It tops out at mid 13's at 2000 RPM before any extra load is added (AC, Lights etc). It usually returns to 14.4V after a restart.

Countless posts here suggest this is normal but on the evidence I can't agree as I have no insight to any info on how the alternator and voltage regulator function and if there is any voltage regulation based on temp or battery voltage.
I don't have any other voltage ranges the alternator charges at and even at the lesser voltage, the battery seems to be at 100% at Days end.

My logger did show that when I started a previous trip with 81% capacity, after 7 hours driving it had reached 92% but that was supplying the running current for the car with lights and AC etc plus charging the battery so it did seem acceptable without any calculations on alternator output vs total load.

Does anyone have any insights into the way this alternator and regulator function? I'm leaning towards the voltage regulator being the cause of the varying voltage but it's a bit premature to jump into a change if that is possible if my situation is in fact inside the normal parameters.

Petza914

The lower voltage upon starting after coming off the battery maintainer is normal. Both my Cayenne and my 997s exhibit that behavior usually showing 13.6-13.8 volts. If I don't put it on the maintainer, then I see 14.2-14.4 bolts so the car knows the battery isn't full and increases the charging voltage to it.

From your description, maybe the car only checks the battery condition and determines what it should be charged at upon initial start up, so after you drive a bit with it charging in the 13s, it realizes on the wxt start and charges at the 14s for that stint. That would mean your next stint after charging at 14 might start in the 13s again. Is that what happens?

I personally don't think you have a problem

IchBautAuto

Thanks, really appreciate the reply. I'm a sucker for this generation of vehicles from the VAG family and have noticed that whereas a 2000 model has barely any issues with battery life, every year on from there has an incremental increase in electrical consumption. The issue as always is trying to become informed as to where the consumption is most focussed, it's a big secret.

Without any battery monitors the GTS seemed fine, the voltage indicated that it was charging at the appropriate time and my driving habits kept the battery mostly 80% plus so no issues. I had my recent starting issues that commenced this whole series of questions and adding the battery monitor opened up a can of worms as to electrical consumption and charging rates that is not evident from a casual glance.

I had mulled over the voltage regulator and on reflection it did seem unusual that the voltage was still being regulated in two distinct bands and no other condition was evident, so a defect there was less likely although nottotally out of the question.

I'll leave it as is and continue to watch and see however there is nothing that is impacting on performance other than being super aware that trickle charging is a requirement in my case.

Petza914

I leave 6 Porsches on Battery Tenders all the time, even the ones used pretty regularly (at least once per week). Makes the batteries last a really long time. Got 12 years out of one of my AGMs, have another that's 9 years old, and a few over 6 years old.

IchBautAuto

Yep, there was a time when I was involved in lead acid battery maintenance (40 years ago and batteries weighing a ton each) and there was a continual routine but my earlier cars batteries would in effect be laid off as there was no house load but by the 2009 model it has become crazy stupid.

What I saw today was a bit confusing, the gauge on the battery briefly read about 0.5V lower than the dash gauge. Normally the monitor directly connected to the Pos & Neg of the battery, the battery logger connected to the under bonnet jump start connections and the dash gauge all read within 0.1V compared with a pro DMM.

I have dedicated trickle chargers for each car and several more powerful chargers should I need them. CTEK or Victron, can't make up my mind whichI prefer.

Ldino21

i had my 2008 S on a Battery Tender regularly since purchased and slowly the battery holding a charge got worse and worse. Finally i got an AGM battery thinking that would solve it. Nope

i finally said to myself something is draining this battery, bit the bullet and took it to the dealer. First thing they came back with was the driver door look would stay in open position even when locked. That solved one problem but system was still draining, eventually figured out it was Fuse #41 the Kessy system, now fixed i havent had the car on the charger for 3 weeks with no issues.

IchBautAuto

Thanks, I am keeping an eye on the Kessy system and so far it's OK, I think. I doubt I could leave the car without a trickle charge for 3 weeks though. Possibly, when I did leave it for an extended time the first indication was the start was laboured and occasionally I needed to start twice to get it going. The tailgate would always work so it couldn't have been radically low. If I take it off charge when fully charged it will read 12.7V 24 hours later and gradually decline with time. Nothing drastic like a major parasitic load.

The battery monitoring system has been both a godsend and a curse. You can keep a very detailed eye on the battery and get it on the trickle charger in plenty of time. I don't just rely on the standing voltage but more on the cranking voltage. The downside is the voltage fluctuations can be a bit concerning. The actual readings are all what you should expect if you factor in all the electrical loading as you activate various systems but nevertheless it's eye opening to watch the voltage drop from 12.7 to less than 12.2 by the time you have unlocked, seated, seatbelt on and ignition on. If you just shut the door once seated and don't put the key in, you can then watch the voltage slowly climb again as systems go off load.

A self study program like VW have would be great to understand the systems that run all the time, those that become active when the key is inserted, ignition on and when running. It isn't info that I have found easy to access.

Metal-Chicken

Wrong thread!

IchBautAuto

An update. I tried a trip without using my sidelights. Interesting that the voltage issues went away. Removed and cleaned both headlights and tail lights with a hair dryer to remove any condensation. Cleaned and lubed the plug contacts and am now in the middle of a 1250Km trip and I get consistent 14.4V at the battery.
I haven't had any of the voltage fluctuations mentioned earlier. Once I get home I'll delete the alternator fault code and see how it goes from there.