3 days with the car sitting and the voltage is down to 8.7V. How should I proceed to chase this drain? Should I assume my alternator is actually charging the battery when I drive?

 

There is a easy way to see if the alternator is charging the battery. First you need to get a DC voltmeter. Start your car, set the meter to 15 volts DC, attach the negative lead to the negative battery post and the positive lead to the positive battery pole. you should see the voltage rise as a surface charge builds on the battery. It should rise up to and regulate at 13.6 to 13.8 volts. If it does your alternator is okay. If not head to Advance Auto and they can check the alternator and battery more extensively for free!

 

You can have an alternator charging, but it could still be bad. If one of the rectifier diodes in the alternator is bad, it will pretty much drain the battery overnight.

 

You are right! However the output voltage of the alternator will not be between 13.6 and 13.8 volts. The diode would be shorting or partially shorting and it will attenuate the amplitude of that phase of the output.

 

What's the likelyhood that an aftermarket electrical accessory is the source of the drain? ie, air horns, strobes, nitrous kit accessories.

 

Unless they're on I don't think they would do anything. Now if you have an aftermarket alarm w/pager that could be a problem...
-Cyrus

 

Karguy,
I am impressed! I stand corrected; I should have read your first post more thoroughly.