Boxster not charging?

[44mod]

2002 Boxster S won't start after driving. A long drive will discharge the battery but it can sit in the garage indefinitely and the battery is still good so I don't think I have a short unless it is only while the car is running. The battery is new and I have tried 2 different ones. I have removed the alternator and had it checked at a local O'Reillys and thely said it checked good. I thought I probably had a bad voltage regulator but now I"m lost. Any suggestions? Do I trust the O'Reillys test? Maybe I should change the regulator just to be sure before I put this thing back together. If I cant fix this I will have to tow over 200 miles to the nearest dealer. Thanks in advance for any help.

[JFP in PA]

The best way to evaluate this is with a battery load tester. This is a device that can check the battery's static voltage (should be around 12.5V or so) as well as the system voltage with the enigne running (should be ~14.5V). Its biggest advantage is that it can apply a 130A load on the battery which simulates trying to start the car (you apply the load for 15 sec. and what the battery's voltage output). We recently had a 911 in the shop that was doing exactly what you describe, a dealer had recommended a new alternator, battery, and starter were needed (read big $). The battery static voltage looked fine, as did the electrolyte gravity (meaning it was fully charged), and the alternator was putting out ~14.5V. But the car periodically refused to turn over. The load tester said the battery failed under the simulated load (probably an internal mechanica fault that develops under the load). We put in a new battery and the car has been fine ever since.

Find someone near by that has a load tester; or consider buying one (the only cost about $50 and work on anything with a 6 or 12V battery, so it's a nice add to any toolbox)....

[44mod]

Thanks for the info, I will be buying a load tester if I can find one. Is there anything else I should check out before I reinstall the alternator?

[JFP in PA]

Check the level of the battery's charge with a cheap hydrometer (less than $5) from and autoparts store; and check the level of your electrical system's draw on the battery without the car running (should only be a couple of mAmps).

Edited March 13, 2010 by JFP in PA

[rshon]

Try putting a voltmeter on the battery. With the engine off, it should read somewhere above 12 volts. When you first start the engine, it should jump up to about 14 volts, and then gradually (over about 15-20 minutes) the voltage will go down slightly. If it doesn't do these things, try replacing the voltage regulator on the alternator. Much cheaper than a new alternator...

[44mod]

Anyone have a good source for the correct voltage regulator?

[JFP in PA]

It is a common Bosch unit, used in several makes, including MB, Audi, VW and Porsches. Check dealers and auto parts outlets............ Edited March 13, 2010 by JFP in PA

[JFP in PA]

Try putting a voltmeter on the battery. With the engine off, it should read somewhere above 12 volts. When you first start the engine, it should jump up to about 14 volts, and then gradually (over about 15-20 minutes) the voltage will go down slightly. If it doesn't do these things, try replacing the voltage regulator on the alternator. Much cheaper than a new alternator...

A common volt meter is always a good starting point; however, a load tester can do the same things as a volt meter, as well as test the diodes and regulator under high current draw conditions, and can also put the battery thru its paces as it would during an attempt to start the car; things that a volt meter cannot do......... The load tester is a much more flexible diagnostic tool.

[wahaneebelly]

Definately sounds like a dead cell or possibly even two as the voltage has dropped so low that you can't even pop the hood. Take a 9v battery. The spacings of the terminals is correct for the transponder. Turn the battery one way - + is to +, - is to -. Turn it the other way, and + is to - and - is to +. Voila ! That's how you put one to "sleep" to preserve the battery.