Ciamaichelo

Over the past two months, I have experienced several dead batteries in my 2005 911 Carrera S (3.8L 997 manual). My battery is less than a year old and it passed two separate test at Kraigen and Autozone. After charging the battery, it will discharge after 4-5 days of driving to about 60%. At that time, the car will struggle to start and eventually fail to start. The battery test OK with a voltage of 12.6. With the car running and high beams, fan and radio on, the battery pulls insufficient voltage to charge or pass the alternator test, using a $15 alternator testing tool, my battery charger or the alternator test at Autozone.

I changed the alternator with a new OEM Bosch alternator and charged the battery to 100%. Thinking I solved the problem, I drove for a week and again the car was slow to start and next time failed to start, requiring a boost.

I then installed a new battery, thinking the bad alternator and frequent discharging killed my old battery. I then tested the new alternator and battery at home and at Autozone. Again, with the car running the battery still pulls insufficient voltage to charge the battery and the alternator tools also state low voltage output. I assume the voltage regulator is part of the new alternator and I disconnected and charged the battery prior to installing the new alternator.

What other components could cause insufficient charging voltage from the alternator to the battery? I read on 6Speed that a bad alternator cable could be the cause. Is there a fuse somewhere? or burn out cable? Any ideas or help would be greatly appreciated.

Thanks,
Chris

dshepp806

Cables/connections can become resistive, for sure.

Are you sure that you don't have a current drain somewhere?

Doyle

theiceman

Autozona Alternators frequently are Crap . I am surprised you would put an Autozone part in such a recent model Porsche. Did you not consider having your existing alternator rebuilt. ?

Anyway I don't know what test equipment you used but you should be pulling about 13.5 volts across the battery with the car idleing . if not I am sure it will be your alternator died.
The water cooled Porsche Board should have more info on this. I am not sure what model you have whether it is a 996 or 997 but this board is for 911s . The guys over there will have more experince with your model.

ivangene

Most places will check your charging system for free... its easy.

There is also a way to check the draw when nothing is on

lastly even a good battery wont always start a car with a bad starter, have the started checked for draw at crank up....

and - go to the 996 board (or 997 if your headlights are round) Those guys will be a good source of info though there is nothing special about a battery/alternator problem.

lastly, you can waste a lot of money buying parts you dont need, if you are not able to find it I think actually having a real Porsche mechanic look at it might be cheaper in the long run

Ciamaichelo

Thanks, I saw the 997 board after I posted this and then re-posted it there. The alternator was changed with a New Bosch Factory OEM alternator from Napa, not Autozone. It is identical and NEW, not refurbished.