2003 Mercury Sable Battery dies after sitting 24 hours

My 2003 Mercury Sable has recently had issues with the battery dieing after not being driven every day. I have replaced the battery and have had the battery tested and it tested fine. I have also had the alternator tested at several 3 different places. Two said it was fine and one said it was functioning at 55 amps and it should be putting out at least 110 amps. I have also tested all the fuses and all are fine. I tried unhooking the battery over night and reconnecting two days later and the car started right up but if I leave it plugged in over night and try it a day and half later the car will not start. The heat blowers, radio and dash lighting all works perfectly as does in the interior and exterior lighting (no dimming at all). I just can’t figure out what could be draining my battery. Any ideas???


How old is the battery?

If it’s older than 5 years, just replace it now. it’s best days are in the past

The next thing to do is perform a parasitic draw test

A note about the alternator . . . if your battery is marginal or bad, there’s no way the alternator can do its job properly. The battery is the foundation of the car’s electrical system.

Based on the fact that the car starts, if you leave the battery unplugged, leads me to believe you’ve quite possibly got a draw

One more thing . . . how is the belt and belt tension?

The current draw may be from the alternator. Testing it by disconnecting the main power cable from the alternator is kind of simple; it’s the one that charges the battery; so it should be thicker than the other cables on the alternator. Pull the cigarette lighter fuse later if the alternator test doesn’t work out.

You said you replaced the battery so I assume it was replaced with a new one. Are you battery terminals in good condition?. Are they tight and clean?. No corrosion?

Using a multi meter test the battery terminal voltage. This is Pos to Neg terminals. A fully charged battery should be 12.65 V. A 75% charge is around 12.40 volts.
When the car is idling the voltage should be 13-14.5 volts. This will tell you if your alternator is able to charge the battery. Turn on all accessories and it should be 13V or more. You may have an intermittent issue and this will not pick it up.

It sure sounds like you have a parasitic drain.
Common sources in this car are the factory alarm system, a cassette or dvd stuck in the entertainment system.

Make sure all interior lighting is off. This include the bulb in the trunk and glove box.

You may want to remove the bulbs for a few day temporarily to see if that matters.

Google on testing a parasitic drain. You will need to place a multimeter in Amp mode inline with the positive battery terminal. This is your next step if you cant find anything.


Not to rain on your parade . . . but the amp meter is placed in series with the negative battery terminal

It is not my parade man! Every document or video on this I have seen says the positive.

Can you explain why it may matter?
Hey I am always open to learn something new here.

Assuming the battery is good (being new does not always mean good) I’d say there is a parasitic draw. Make sure the trunk light is not staying on and don’t laugh; it’s more common than you would think.

You might avoid that place who told you the alternator should be putting out at least 110 amps.
An alternator that does that will only do it for a few seconds before going up in smoke.

Doing a current test can be done using either pole of the battery but the reason the negative side is usually used is due to safety reasons. If the test connections are placed on the negative side then if any of the connections come in contact with chassis ground nothing will happen, except perhaps the meter may get bypassed and have no reading as a result of that. But imagine what would happen if the positive side was used and any of those connections came in contact with ground. Need I say more?

Like others have already said, there appears to be an excessive parasitic drain on the battery while the car is parked and a current drain test needs to be done. Normal current draw on the battery should be less than 50 milliamps when systems are in the sleep mode.

Cougar, good answer and thank you.

Christian, Good luck in testing for you drain. It is very tedious task but not hard to do.

I have nothing against the internet, and youtube videos

However, there are a lot of guys out there giving advice which is not entirely correct

Or, at the very least, it’s not the best way to do it

Scotty Kilmer . . . need I say more?

You can also start pulling different fuses each night until you find the one that causes the problem.

Do you have any of the following: an aftermarket security system, an aftermarket audio system with a remote sub woofer amplifier, a factory subwoofer amplifier. or a remote starter?