I need to know if my problem is my battery or the alternator

The car had a new battery installed 1 year ago / 7k miles.

Since last week when I had my Zeitronix unit installed, the install shop had my doors, hood and spoiler all open for like 8 hours at a time. When they went to start the car at the end of the day, the battery was dead! We jumped it and it was fine. I drove it home (20 minutes) or so and it was parked in my Garage for a week without driving it. I started it up with no Problems on Monday (week later) and drove it all day and again today with no problems until I had my Detailers wash my car this afternoon. They left the doors open for like 45-60 mnutes while the detailed the inside (door & doom lighst on) and they tried to start and the battery was dead. They jumped it and let it run for 5 minutes and turned the car off again, it was dead once again. We jumped again and I drove it home (20 minutes of driving) and now it starts ok.... There are no problems when I am driving.....

I stopped at Autozone on the way home so they could test it and the Alterator only tested at like 13 Volts at 2k rpm and the battery was at 12.5 - 13.0 volts...

Is it my alternator or my batter?

Please advise and sorry for the long novel!

 

You want to look for Amps on the alternator output, for the most part. 13-14 volts is good, but if its only 1-50Amps, alternator isnt giving the battery a good charge. Normal 996/986 alternator amp rates should be around 100, 90-110 or so, this recharges your battery. For the record, the cayenne uses a water cooled 220 amp alternator...

 

It is not likley that the alternator is bad from what you describe. Most probably the battery's capacity is diminished.this happens when they fully discharged a few times, Common on these cars because they sit and drain from the imobilizer system, doors open from your service. I would go for a new battery not OEM .Make sure connections are clean and tight.

 

Keep the opinions coming! I am hoping its just a battery as well!

 

I also think it's the battery, just had the same things happen to mine. I replaced it with a yellow top Optima and the problems went away. I don't think a weak alt. is going to put out 13 volts at 2k if it's on it's way out.

 

Just the battery.. had the same thing happen to me...

 

OK since everyone says battery (which by the way I would get a new one at this point anyway) I go with the alternator. these alternators fail in two ways either completely, or what yours is doing low end failure then it goes.
Have a dealer check it, I really think that is your problem, it is exactly what mine did and it then completely failed at the track!!

 

Sounds just like my situation last week. It all started after a couple weeks in Hawaii and a cold garage; then prolonged work done on the car (radar) with the door open; add in a lot of errands (ergo starting the engine multiple times).

I was spooked, but it was as simple as a battery swap and she turns over like new now. My tech advised I had the original battery and it was time to put her down.

VB

 

Tom - What did the new alternator cost you with install?

What are some ways I can test to see if its an alternator or a battery?

 

I would almost think battery too, but the battery was replaced 1 year ago?

 

The battery is easy to test, just pull it and take it to Auto Zone and have them test it (FREE) for cc amp output. I would bet it's the battery.

 

I would say it's the battery as it charged once after you had it running, which would suspect the alternator is working fine. If you run a battery down a few times it will more than likely not be holding the charge. I would just go and get it checked before you spend money buying both!

 

996TT Stevo is correct, you can jump a car with a dead battery and get it up and running. However, if the alternator is defective it would not charge the battery for the next start; it's the battery.

 

Anywhere with an amp/volt meter to check the alternator output.

Rebuilt alternators can be had for $250. Of course I got the new warrantied porsche one about $650 and install I think cost 1k

 

1k total with install or 1k for just the install alone??