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I have a 2008 F150 that the battery drains after sitting 4 days or longer. This has happened about a dozen times since I bought the truck and the dealer could never figure out why. Warranty is up now and it is STILL happening! I had corporate office insult me by telling me everything "checks out" and it is just like a cell phone. If you don't periodically charge it up, the battery dies. I asked her where I was supposed to plug my truck in at night and there was silence on the other end. I am 62 and have never had a car or truck do this from just sitting. The dealer insists everything checks out. Any clues on how to handle the dealer?

 

Any aftermarket electronics? Including dealer installed alarm system.

Does the battery load test okay?

Alternator is a big suspect because when the VR goes bad it will pull some Ma's and kill off the battery.

You could always unplug the VR connector on the alternator charge the battery and let it sit for a few days if it does not drain you found the issue.

 

I had a new stereo system put in a year ago, but the problem was ongoing before then. Early on they had to put in a new computer.

As to testing, I have left that up to the dealer as they are the supposed "experts." How can I argue with them? They are adamant that everything checks out. I did have one service rep--not the service manager--make an admission that this was a problem with Ford and Nissan trucks. Whoa! Of course, when you talk to the service manager, the response is "I've never seen this problem before." Yeah, right.

 

Stop by Autozone or whatever parts stores are near you and they can load test the battery and also the alternator. You can put an Amp guage on the pos battery cable when you unhook the pos cable and check for a amp draw.

 

Thanks for the offer, but Ford has done very extension testing as of today. They tell me everything checks out. They have requested that I leave the truck with them for 4-5 days to duplicate the drain. We'll see what happens.

 

This problem is either a problem with the battery/charging system, which you say has been checked out, or a parasitic drain on the battery. You can check for a drain by disconnecting the neg battery cable and putting an ammeter in series to the battery. If you see a excessive current flow, start pulling fuses until it goes away. Then troubleshoot the suspected circuit to find the cause. DO NOT try to start the truck with the ammeter connected.

I was told by a Ford technician that these trucks should be able to sit for at least 3 weeks before the battery drains down.

 

Thanks. I am collecting all of what seem like relevant comments and taking them with me when I return the truck. The service manager seems as concerned about tracking this down as I am.

 

You might apply the lemon law if you have gone back to the dealer several times regarding this same issue, you should do some research, and keep track of the work orders and any receipt from the dealer.

 

Funny how opinions go; I was told by a Ford tech that a drain will happen in about 10 days in warm weather and 7 days in cold weather. Mine does about exactly that so when I know that it is going to set idle for a week or so I just disconnect the negative battery cable and the drain does not happen.

 

There are some low drain systems like the security system that are active when the truck is off. I wonder if you may have a border line battery that this little drain would take it down far enough. I'm guessing but the dealer may not have load tested the battery. They can seem fine but if it has a bad cell a load test is the only way to find it. That's why they're known as "mystery boxes." More ammo for you when you go back I would mention it.

 

No security system. 2nd new battery Ford has put in. I do have a kill switch in the cigarette lighter. It stays "on" most of the time.

 

I'm guessing it's the stereo. You mentioned a new one was installed. At least on my 2008 there appears to be 2 circuits going to the stereo. One powers the amp, etc. and automatically shuts down when the circuit module it's on turns off. This happens after a delay period from when the key is removed from the ignition. The other allows you to get cds out at anytime without using the key. That one may be hot always so if you switch the two in changing the stereo there is constant power running to the stereo. Or- it could be wired correctly but your cd eject mechanism isn't shutting off which will also result in a parasitic draw.

My constant drained battery turned out to be the cd eject mechanism. Either way this should be simple for a tech to figure out-

 

Interesting. I hesitated to mention the stereo to the service manager as I figured they would look for any "out" since I am past warranty. "Nope, we checked out your stereo." I will follow up on this, though. Maybe the simplest thing would be to just disconnect the stereo and see what happens. Thanks for the tip.

 

X2 on the above. Any more then 50mA and it wont last a day or two.

 

I am going to disconnect the stereo system the next time the truck is idle and see what happens.