2004 V6 Battery died @ idle with AC on

[traditional85]

Last week I was sitting in my car for about 30 minutes in the Texas heat with the AC on at idle. I turned off the engine then tried starting it about 10 seconds later but got the clicking sound as if the battery died, and it did. Had to get it jumped and pretty much have been driving with the AC off since then. I just recently took some voltage readings at various stages with the cigarette adapter voltage meter. The car starts and runs fine, but can anyone add their feedback on these readings to determine if it's a battery/alternator/voltage regulator issue? I know a lot of these readings may be irrelevant but I'm trying to provide as much possible information as possible. I haven't checked the readings at the alternator posts yet because it's been raining non-stop. The alternator is most likely stock but the battery is 6 months old. No electrical modifications.

Off -> On (idle) = 12.4 -> 13.8

Idle in Park @ ~750rpm = 13.9
Idle in Park @ ~750rpm w/ fan = 12.8 -> 13.7
Idle in Park @ ~750rpm w/ AC = 12.5 -> 12.4
Idle in Park @ ~750rpm w/ lights = 12.2 -> 12.6

70 mph @ 2000rpm = 14.1
70 mph @ 2000rpm w/ lights = 14.0
70 mph @ 2000rpm w/AC = 14.0

45 mph @ 1500rpm = 14.1

 

[wmburns]

It's obvious that your alternator isn't putting out enough at idle. Note, 13.8 is the LOW end of the normal range. Below 13.8 the battery will not really charge. Short periods of idle will not hurt anything. But as you have found out, over a long period the battery will discharge.

There are several ways to look at this. Here's some information that might be of help.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

The benefit of dissecting the workings of a charging system is fixing exactly what is wrong with your car. If you are handy you can repair your own alternator and save some real $$'s.

Another way to look at this is an alternator is part of a "system" and who cares what's wrong with it because the "fix" is to replace the whole alternator. If this the way that you think then have the alternator tested. Most auto parts stores will test alternator and batteries for free. If the alternator fails the test then get another. Problem solved.