2008 Mercury Mountaineer 5 day battery drain

I have a 2008 Mercury Mountaineer with a brand new battery. Under normal driving conditions (commuting to and from work once a day, weekend road trips, etc) there are no problems whatsoever, no problem starting etc. However, twice within the last six months, I have traveled for business, and upon my return, the battery was completely dead. No turnover, no lights, no nothing. The first time it was about 4 days, second about 5 days. The first time I had the battery replaced, as it was the original battery, but then it happened again. The local Ford dealer had the car for a few days, let all the modules go to sleep and could not find an issue. There were no lights left on, nothing plugged in. Alternator, battery, etc all check out fine.

The battery just seems to get drained / die if it is not driven for more than 4 or 5 days.

Any ideas??? Please help! Thanks!!


There has to be a parastic current drain on the battery as the vehicle sits for an extended period of time. These can be hard to find sometimes.

I had a Lincoln come in where the battery would drain down. It was discovered that light control module would turn the interior lights on randomly. The vehicle could sit for hours without the problem and then the interior lights would come on for random lengths of time and then turn off for random lengths of time. This would occur for just ten minutes or for as long as an hour. How I found this out was I went into the shop when the lights were off when I noticed the vehicle interior lights came on and then shut off.

This is why these are called FRED’s. Frustrating Rediculous Electronic Devices.


+1 for @Tester.

Thanks @Tester, that sounds like it has potential. Any suggestions on where to direct my dealer / local mechanic to look?

You can do some checking. Glove box, or other interior lights could be the problem. They sell a parasitic tester that you plug into the fuse positions to find the problem. You could pull the fuses yourself and see if it fixes the problem.

Yeah @knfeimore there definitely isnt anything that is left on, if its a problem, its probably how Tester mentioned above, something that randomly happens during a non-driving 5 day period. That’s the only problem with the fuses - in my understanding, in order to understand which fuse it is if that’s the problem, you have to pull each one and wait 5 days since that’s how long it takes to die…

When you leave for an extended period of time, how far away is the ignition key from the vehicle?


It would be nice to know how much current was being used while things are in the sleep mode. The current draw should be less than 50 milliamps I would think if things are good but it appears the current demand goes up after some time period of being parked as you should be able to park the car for weeks without any trouble. I would guess this problem is due to one of the electronic modules in the car isn’t staying in the sleep mode for some reason. Perhaps a door switch isn’t working correctly and it is closing making it look like a door has opened.

Let’s do the math. New, fully charged batteries have about 30 amp-hour capacity give or take. 5 days is … hmm … 120 hours. So the OP’s car is averaging a current draw of about 30/120 = 1/4 amp = 250 mA. As @Cougar says, 50 mA or less is what would be expected when the car is parked and everything is turned off and 1/2 hour has passed so that all the computers have gone to bed. So there is indeed something amiss.

The first thing I’d do is ask the mechanic to confirm by DVM measurement that there’s a current draw of 250 mA constantly going through the battery ground lead when the car is parked, key off, all lights off, and computers sleeping.

If 250 mA drain is confirmed by measurement, then the individual circuits can be disabled by pulling fuses one by one until the problem circuit is discovered. At which point the solution is near.

If not, the measured drain is 50 mA or less, then the battery must be self-discharging by itself. This can happen if battery is no good (possible, but unlikely) or the surface of the battery becomes coated with an electrically conductive surface film of some kind or another. Battery fluid for example, if it coats the outside of the battery, can cause this.

A couple of other ideas. Alternator diodes can go on the fritz and cause this. Often as a result of either jumpstarting your own car, or using your car to jump start somebody else’s car. Maybe unplug the alternator next time you park it for 5 days and see if that prevents the battery drain. If so, you’ve found the cause.

Any added non-OEM electrical equipment, like audio systems, or esp car alarms should be first suspects. If the OP has any of these installed, see if unplugging them solves it.

I can’t speak for your Mountaineer but with both of my Lincolns and the Lincoln my youngest son used to own there is a significant current draw when the key is off. Those cars all pulled about 700 Milliamperes for up to an hour before everything goes to sleep and the current drops down to 100 MAs; give or take.

Needless to say, an iffy battery could give up pretty quickly on a number like that but seeing as how you have a new battery you might consider having the parasitic draw checked. Determine what it’s pulling immediately after shutoff and what it’s pulling a few hours later to make sure that the current draw is not up in the mid or upper 3 digit MAs range.

You’ll find an intermittant like that through luck only. I had two different Rivs that had a drain problem. Went out to the garage one night and the interior lights were on. The door knob that turned the interior lights on was shorting out once in a while and draining the battery. On the other one it was a short in the electronic level control unit. Spent an hour or so looking for a drain and then all of a sudden the test light lit up and went out when the ELC was unplugged. Now it also happened that the wife didn’t close the trunk completely at the airport so the light was on for a few days and that did it too.

@Tester - Key is inside the house sometimes, sometimes with me in another state.

@Cougar - The car is only running about 30 milliamps in sleep mode, so even less that the maximum. All the modules have been tested, put to sleep and woken up, etc., and there were no indications.

@GeorgeSanJose - I think the battery is good, it was replaced by AAA about 4 months ago and has been tested, and the situation is still occurring. There is an after market speaker system, but I was told since there is not an actual amp, and they’re just speakers, things should be OK. It is still something worth considering though. The alternator supposedly checked out, but I’m not sure how thorough the examination was, so unplugging it is a good idea.

It seems as there is no typical silver bullet here, and that it will just take a lot of trial and error (and luck…) to find the root cause.

If it’s not an intermittent, what about the possibility that the new battery is not up to par?
Just because it’s new does not mean that it’s good so maybe a load test of the battery might help.

This is mentioned only because I’ve seen a number of premature battery failures. The quickest failure was one involving a new battery (Die Hard) that I purchased and which went completely belly-up the very next day.
It could be charged and started but if allowed to sit for 5 or 6 hours that was it. Dead; and there was no parasitic current draw at all. The battery could sit on the bench and go dead after recharging.

I have had three occurrences like this.

  1. Glove compartment light staying on (only noticeable at night, thru the cracks)
  2. Bad battery–unable to sustain a small drain.
  3. CD motor continues to turn after CD ejected.

The 30 milliamp current draw while in the sleep mode is a very reasonable number alright. The battery has been replaced with no improvement with the trouble so that isn’t the problem. The problem with the CD motor that @melott mentions is a good suggestion and does happen but since the current draw is normal that isn’t the case here. Since the current drain is within normal specs it seems to me there are only two possible ways for the trouble to happen. Either an electronic module is changing state while in the sleep mode or the trouble isn’t really due to a current drain. The real problem might be due to a intermittent connection problem with the main power supply to the distribution panel under the hood. Power isn’t getting to it and making it seem that the battery is dead. Are you sure the battery was dead when the trouble happened and verify that by checking the battery voltage using a meter?

Battery voltage might be normal, but drop to ZIP under any kind of load.

Yes, that can happen alright but the OP has already replaced the battery and to have a second battery cause the same trouble seems pretty remote to me.

It is possible of course the new battery is no good. Sometimes this happens. It happened to me in fact. But still, for a new battery, it is unlikely. In any event the battery’s condition (good or bad) can easily be determined by a simple load test. Most retail auto parts stores will do that test for free. An alternator can test ok but still drain the battery. The test is for how much electrical power it produces, not whether it drains the battery or not. So unplugging it is worth a shot as a test. But the measured sleep-mode drain current of 30 mA suggests it isn’t a alternator-caused battery drain. So it appears to be one of four possibilities:

  • The new battery won’t hold a charge (charge it up, then have the battery tested.)

  • The new battery is self-draining. (take it out of the car, charge it up with a battery charger to 100% full charge, let it sit for a week, then have it tested). Note: Sometimes just cleaning the outer case of the battery with a baking soda/water mixture, then rinsing with plain water will fix this.

  • The car’s computer is leaving sleep mode for some unknown reason & is draining the battery then, but so far this event has not been captured by a battery current test. (There are some DVM’s that can capture an event like this unattended, but you’d need a pro for help to set up the test.)

  • The battery’s connection to the rest of the car is bad for some reason. A wire is broken somewhere, etc. I had this happen to my Corolla, a freak thing, where the battery was leaking acid, which decanted down one of the wires, and opened a splice deep inside the wiring harness. (Probing the voltage of the various circuit voltages under load can prove/disprove .)

I think this site might help.