Slowly dying batteries

[Gargamel]

94 Mustang V6

Battery slowly dies after several (5 days or so) non-use of the vehicle.

Recharging the battery gets us back up and running, but I'm trying to figure out what's going on.

Panel in car shows good voltage to battery while driving but I haven't pulled out the multimeter on it yet to check voltage from the alternator.

If you drive it daily, we seem to be good, but its when it sits it seems we have a discharge somewhere.

Any ideas?

[VaderTT]

Use a multimeter and pull fuses until you find the draw. I had to do this last week on an 06 x3i. 4 fucking huge fuse panels!!

[JC316]

Check the visor mirrors. I near went nuts looking for a battery drain like that and the stupid vanity lights were on.

[talisman]

Does it have an aftermarket alarm? If not, it probably has a bad diode in the alternator.

[Cooter]

How many batteries does a 94 v6 have?

[shumpertdavid]

How many batteries does a 94 v6 have?

Lmao, it's the diesel version......

As stated above, you have a draw/drain somewhere in the system. The vanity mirrors are a good possibility as are trunk and glove box lights if applicable. The alternator is also a likely candidate too, a volt meter that allows amp testing is what's needed to correctly test the system.

[YALE]

dying

[astang95]

definitely check for an aftermarket alarm, I had one on mine and it started slowly killing my battery

[rainman64]

I would do a amp draw check with a MM or a old school test light. Make sure you wait about 30 sec to make sure things like delay door lights go out. Was in the car audio industry for over 14 years and during this time had people and dealerships bring vehicles in all the time and almost always blame the aftermarket alarm as the issue, even had one customer say his mechanic told him that he was 100% sure it was the alarms fault, checked the normal problem causes and it was the alt. was to blame, and it was a Ford vehicle. At that time I went and told the customer that he needed to find a new mechanic and that it was not the alarm that was his problem.

[shumpertdavid]

Rainman, while this particular car should be good for the electronics to go to sleep in 30 seconds to a couple minutes, the newer stuff isn't that fast. They can take 30 minutes to a couple of hours for everything to shut down. I've always heard about using the test light to check for a draw but never found it to be terribly accurate. A meter is usually the best way to go. As little as .1 amp can drain a battery dead over a few days.

[Gargamel]

1 battery... not set of...
Noted.... dying....

Thanks for the help all, agreed I've got some sort of parasitic battery drain.

I'm leaning toward the alternator and the vanity lights already have some issue with them, so they don't work anyway.

Just too cold out there to be screwing with it lately.

This weekend looks like it might be warmer for this kind of stuff and I'll start pulling fuses.

[sig239]

How old is the battery? Hard to find a good one any more, seems like every year and a half I end up putting a new one in the wifes car.

[justin91lx]

Check the visor mirrors. I near went nuts looking for a battery drain like that and the stupid vanity lights were on.

My Fox had the same issue. Sit for a week and went to crank it and nothing. Didn't see the issue till i drove it to a buddy's house one night

[Gargamel]

I think I found the draw this weekend.

It seems to be something with the integrated map light\compass\rear view mirror assembly. It seems to be pulling way too much draw on the battery after the doors are shut, auto lights click off.

I guess it could be something else in the same circuit or a short, but as soon as I disconnect the rear view mirror assembly, the draw lessens to less than 8 milliamps. (around 30 when the connection is in place)

[shumpertdavid]

30ma is pretty insignificant, but would drain it down over a long period of time. I would think in excess of a couple weeks if the battery were in good shape. IIRC @100ma will drain one in about a week. 300ma and larger are what I consider a large drain.