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Mike Kelly
Mike Kelly, Auto Service Technician
Category: Car
Satisfied Customers: 5471
Experience:  17 years experience as an auto mechanic, foreign and domestic. 5 years running my own repair business.
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I Have a Porsche 911, 996,2001 Carrera, The battery went flat,

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I Have a Porsche 911, 996,2001 Carrera, The battery went flat, there were no indications that there was a alternator problem. the garage suggested a new battery . this was fitted but 2 days later the new battery is flat. can you please advise.
Hello, welcome. My name is***** will do my very best to assist you with your question. I apologize if you have been waiting long for a response.

Even though there were no warnings of a alternator issue, has the alternator been checked?
Customer: replied 3 years ago.

Hi Mike, No the alternator has not been checked, when the car is running there is no fade from the lights or any other components, its only when the car is left over night that the battery drains, I have made sure every thing is turned off, even to the point of removing the bulb under the bonnet ,

Ok the next step I would suggest is to have the alternator tested, from what this sounds like the alternator is making the battery slightly weak while driving but not enough to notice. Have this checked and get back to me. Thank you.
Customer: replied 3 years ago.

Hi Mike, had the alternator tested no problem there.

Ok good. While the vehicle is off and the key out, go to the fuse boxes and test each fuse with a test light to see which system is being supplied with power while the vehicle is off, this will point to what is drawing down the battery.
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Customer: replied 3 years ago.

Hi Mike, is it possible with the ignition off, for the alternator to bleed the battery down, Is there not a diode or sum such device between the alternator and the battery to prevent this happening ?

Yes this is possible, for this to happen there would have to be a open short in the harness leading to the alternator.
Customer: replied 3 years ago.

so the bleed from the battery to the alternator cannot happen unless there is a short in the harness, would you say that the alternator is not the problem as an individual component.

Yes I would say the alternator is likely not the issue here.