I have a 1999 Mustang that eats batteries for breakfast, lunch and dinner. The car operates normally as long as you drive it daily. However, let it sit for 2-4 days and the battery won’t even let you “click” the ignition. It is been tested for shorts, cable rubs, and weird levels of battery drain. Everything falls within norms. So far, three mechanics (one an electrical specialist??) have not been able to find the solution. Their best help has been to suggest a cut off switch under the dash that interrupts the hotwire of the battery or to carry a good set of pliers in the glove box. I am not satisfied with either answer. The car will jump off a fresh battery and my son has become an expert with the jumper cables - a surprise bonus. I have been suspicious of the alternator - however, all three wise guys have confirmed that it is ok. Can anyone offer a suggestion to at least point me to a solution. By the way - “Yes” - I have replaced the battery - four times. What are the chances of four bum batteries??
Pretty slim. BUT not impossible.
When your ‘wise guys’ checked for battery drains, etc. was a complete (in vehicle) full load test performed?
IMHO, testing (in vehicle) eliminates the possibility of missing bad ground connections/connectors and bad cables.
There has to be a pretty heavy current drain coming from somewhere. Perhaps there is a long delay after the car is shut off when the trouble happens and that is why the experts haven’t found the trouble. By installing an ammeter in series with the ground lead to the battery the current can be monitored and then see when the trouble occurs. Normal current draw for most cars is less than 35 milliamps. I suspect you have something drawing more than 100 milliamps when the trouble happens.
Yes, they performed load tests and independent fuse tests (are these different?). The last mechanic kept saying, “we couldn’t catch it doing anything; the drain on the battery is well within norms of what it should be (for clock, radio, etc)”. The second mechanic mentioned the ground connections and eliminated the cables as an issue.
I might need help with running the ammeter option - never done it and don’t recall the 3 mechanics mentioning it with the diagnostics.
I agree on the heavy current drain. That is why I am so incredulous that all three mechanics have been somewhat cavalier in saying they don’t know what is wrong… It seems like a huge white elephant is there somewhere draining the thing…
The last mechanic did mention milliamps and said that the car measures pulling about 7. He did not say anything about a delay. They had the car about four days and had some sort of diagnostic on it the whole time. I assume perhaps this was an ammeter. My best guess would be that the last mechanic covered this base.
Tough one. Here’s a shot in the dark: when they check for the parasitic draw on the battery, they have the hood open, right? If your car has a hood light on the underside of the hood, they probably remove the bulb before they do the parasitic draw test on the battery, or else they’d get a “false positive”.
Then when they’re done, before they close the hood, they put the bulb back in. Do they then make sure the hood light goes out as they close the hood?
You say you’ve replaced 4 batteries, but were you absolutely sure the old batteries were shot, or were they just discharged?
Ask the 3 techs exactly how they tested the charging system. They should have done at least 2 things. (1) With an ammeter measuring charging system output, you should see 90% of alternator amp rating (while a load tester draws current from battery, with engine running at about 2000 RPM).
(2)With engine idling, and all unnecessary electrical accessories off, a voltmeter across the battery posts should read 13.5V or more.
The reason I say this is because in the hundreds of times I’ve checked alternator/battery problems, when the charging system passed test 1 it always passed test 2–until just recently when I came across an alternator that put out great current at 2000 RPM, but failed the 2nd test (alternator not producing current at the lower engine RPMs).
The cutoff switch for the battery might be a good idea–as a diagnostic test, not as a permanent solution. If you install the switch and turn it off when you get out of the car and the battery still goes dead, you can rule out a parasitic draw.
Good luck and please let us know what happened.
The battery cutoff switch is a good idea, but first I would remove the hood, trunk and glovebox light bulbs and see if that stops the dead battery. I have a 2003 Chrysler minivan that the battery went mysteriously went dead on but I found the problem when I was walking by the car two hours after it had been parked and heard the fan start up. It was a bad fan control module.
Another thing to watch out for is a bad connection from the battery to the main power bus distribution panel. A bad connection could make you think the battery is drained since nothing is working. Hopefully the shop checked for that kind of thing. If that isn’t the cause then a parasitic drain is happening and monitoring the current drain while the car is parked will show up the trouble.
I do not know specifically about the the method of how the mechanics checked. As to the old batteries - well, that was really weird. Each time I would take the battery to a new mechanic, they would notice that the battery was Interstate and even with me telling them the battery was new, they would basically say “not a problem, it is under warranty”. To my protestations, each put a new battery in the car. There was nothing wrong with the one they took out except my hungry Mustang ate the charge (weird - on the mechanics, not the car).
I am curious: if it is not a parasitic draw as you suggest with the cutoff switch comment, then what else would crash a battery like that?
Great suggestion on the bulbs. Do you think three bulbs would crash a battery in 2-3 days??? I will try it though.
How can you monitor the car without sitting and watching an ammeter for three days? Is there a diagnostic the produces a tape print out?
“what else would crash a battery like that?” No alternator output, but you said 3 techs checked that, and one was an electrical specialist. My guess is, it’s a parasitic draw that takes a while after you’ve gone inside to rear it’s head, like Cougar mentioned. You said you don’t drive your car that much. Take it back to the electrical specialist and suggest that he park your car outside his shop in the AM, and hook up his ammeter, that measures in milliamps, between the neg battery post and the neg battery cable end. (He will already know this, but run it by him anyway.) Then he can go back to his other work, and maybe every half hour, check his ammeter. By the end of the day the parasitic draw may raise its head. This way he might not charge you any labor–until he sees that you have a draw. Then he will start pulling fuses one by one, to narrow down where the draw is coming from. Hope this helps, KS.
If the trouble is really due to a current drain I doubt you will have to wait more than a few hours to catch the trouble. There are meters made that can record the time and min/max levels also.
Does the 'stang have a key pad on the door and automatic headlamps? Where do you park at night? If the answers to the questions are yes and yes. Try parking with the headlights facing your bedroom window or turn off the autolamp and see what happens.
The key seals can decay allowing moisture in. That can make it “think” you touched a key and turn on the headlights.
A few years ago, my '89 Ford Crown Victoria 5.0L went through this exact same scenario. I even ended up installing a racecar style battery cut off switch under the dash! A couple of months after I installed the switch, the battery went dead as I drove the car home. The alternator was no longer charging the battery. I replaced the alternator, stopped using the battery cut off switch, and have not had a problem since.
My best guess is the alternator was failing intermittently for months. That intermittent failure process somehow included occasionally draining the battery when the car was off. All I replaced was the alternator (which includes the voltage regulator) and the car has been running fine for years. I can’t explain what was going on with the alternator’s circuitry, but an alternator dying a slow death was definitely what caused this problem, at least with my Ford.
Actually, this answer makes the most sense to me. I pulled the bulbs (as recommended above) and nothing to show for it. It is strange that three interior bulbs would kill a battery in 2-3 days anyway. I think I may have the alternator replaced. Someone said above in the email stream that a dying alternator can cause all kinds of weird electrical issues. This is one.
The trouble with disconnecting the battery when you park it is that it will have to relearn all of the adaptive info that the PCM stores. That will mean poor running, decreased fuel economy and higher emissions. It means you won’t pass an emissions check too.
No key pad on the door. Parked in driveway at night. No auto headlamps. In fact, one of the first things I had the 1st mechanic do was replace the switch on the dashboard for the headlights. I bought the car used the the old switch was a little “gitchy”. But replacing the switch did nothing for the battery issue.