Power drain overnight

Hey guys, I am having a strange problem. About a week ago, I had a ten-month-old battery freeze on me because I did not start my truck in about a week. So the store replaced it, but now, the new battery (three days old) is not holding charge overnight. These past couple of days, I have had a total dead, drained battery in the morning! Last night I unplugged my phone charger connected to the lighter, so this time, as far as I know, there was no electric loss, but the truck battery is dead again. I am at a loss here. Any suggestions of what could be happening?

Doing a little research, I found how to check for a Parasitic Battery Drain with a multimeter and pulling a fuse at a time. That reminded me that I also replaced the front lights with LEDs, which all that was required was to plug them in, no extra adapters or extra power required. So I was wondering if those are causing the problem (I installed them as I was replacing the battery). What would it be the fix? I also read that the alternator could be the problem. Is there a way to test the alternator?

you either have some sort of light on or a parasitic drain. check for light on under hood, glove box or a bad brake light switch that might be keeping the brake lights on. they can get stuck on intermittently.

The BEST Way TO Perform a Parasitic Draw Test - YouTube

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You have a parasitic drain. Something electrical is drawing s significantamount of power from the battery when off. Any add on things like stereos, subs, remote starters and similar. Assume one of these is the issue… disconnect it and test overnight.

If the obvious does 't jump right out, have a parasitic drain test run to find the problem. Eric the Car Guy or Humble Mechanic on YouTube have good vids on how to run the test yourself.

Thanks for the reply! As I was editing my question to add exactly that information, yours came along. Please note that the truck is old, and this problem just developed, so the only changes are the new LED lights, and the new battery (the old one froze) -which makes me wonder if the old battery damaged something, like the alternator.


This site gets quite a few posts where LED lights in old vehicles has caused problems . Take them out and see if they are a problem.


Suggest to start w/the basic battery/alternator test: Battery should measure about 12.6 volts before first start in the morning, then immediately after starting the engine, 13.5 - 15.5 volts. You are welcome to post your shop’s measurements here for more ideas. A fully charged battery usually won’t freeze, chemistry of electrolyte prevents it, but when it discharges, chemistry changes; if discharged enough, then it can freeze. So keeping it fully charged is your best bet to prevent another freezing episode.

As far as what’s causing the battery to drain, if basic test above passes, alternator problem not likely. You say you replaced the front lights w/LED version. Do you mean the headlights? Seems unlikely that would cause a battery drain, but anything’s possible. You could measure the battery parasitic current both ways I guess, measure, then reinstall old headlights, re-measure, as a test. If you’re not experienced with electronic measurements using a volt/amp meter, suggest to defer to your auto shop for measuring parasitic current.

Common sense say to first check that all the lights turn out when you park your truck overnight. Interior lights, glove compartment, engine compartment, and especially the rear brake lights. Press the door switches to make sure it reliably turns whatever lights affected on and off. Sometime a door switch becomes “iffy”, and will turn on in the middle of the night when a gust of wind hits the door.

Like I have said before, I have had two intermittent drains. Didn’t show up with a test light. The one after buying a new battery, turned out to be a shorted door handle push button that turned the interior lights on. Discovered it late one night going into the garage and the lights were on. The other was an electronic level control that would short out. After going through everything for a third time, all of a sudden the test light went bright.

Yeah sure check all the normal stuff like glove box and trunk light but just remember it could be a zebra or something unusual.

Thank you for the reply, guys, very helpful.

So the battery reading with the car off was 12.4V; right after the truck started was 14.5V, and about 5 minutes later, it was 13.5V. Then I set it to read amp draw, and I got 0.0815 (I am guessing milliamps, please look at the picture, but then that number would drop 3 seconds later to 0.05 and about 10 seconds later to 0.003. Now, here is where it gets interesting. My negative wire has a smaller wire attached to the truck chassis, so reading voltage from the negative pole of the battery to the ground bolt near the battery, I get 12V. So If I understand this correctly, the chassis is getting current from somewhere. Can it be a bad diode from the alternator allowing the charge to be leaked?

Not likely. Negative pole of the battery and ground bolt are electrically the same thing (on a negative ground car).

Check that again.

I checked several times! I even got a volt reading of 12V, so that is why I took a picture as proof! That ground bolt in the chassis has charge

Is that aluminum foil contacting the + and the - side terminals? If so, that’s a short circuit, which will drain the battery. If the old battery froze, that’s a sign of it being very discharged.


Well as a novice, let’s go back to basics. In order to get a voltage reading, you need to go from pos to neg. Putting the meter on two ends of a pos cable or negative yo will get nothing. So this makes no sense unless you have a dead short and burning cables.

One of the issues with after market leds is that they heat up. So it is possible the socket or bulb got fried and is shorting out. Same as having the lights on with or without a lit bulb. I’m grasping here so I would take those things out and check the sockets. I put leds on my lawn mower with no problems but the lights are not on much.

You may just have a bum battery that is not holding a charge overnight. 12 on a battery is not a full charge. I would disconnect the battery over night to see if it discharges or not. Disconnecting the battery can cause issues but you have already done it several times. Source of the batteries?

I guess once you are back to stock and know the battery is holding a charge, go back and look at the link on how to I’d a circuit with a drain by checking for draw on the tops of the fuses. I used a test light myself, but his system is easier. If you find a circuit with excess draw, then use a schematic to I’d the components on that circuit and take them out one by one to find the bad one

You have to go step by step in an orderly fashion or you’ll get all messed up. Unless you can just eyeball burning wires. Gotta trailer hitch? Wires smashed together?

Either the negative wire is broken or the connection at the battery is so bad that you’re losing 12 volts across it. Or you’re measuring it wrong.
From your picture it appears that you’re plugging your probe into the battery. If the other end of that same wire is at 12 volts the battery connection is TERRIBLE.

The PCM and radio are connected to battery positive with the ignition off. With the negative battery cable disconnected, your amp meter, voltmeter or test light completes the circuit between the chassis and battery ground. This does not indicate a problem.

Get all that tin foil away from there!


It looks like the aluminum foil surrounds a foam pad. I think the foil/foam is a heat barrier. It isn’t clear whether that is an OEM feature or added on by the owner. I agree that aluminum foil touching the battery terminals could cause a short if another part of the foil finds its way to ground. If this is true, it might be as simple as insulating the positive and negative poles at the battery to prevent contact with the foil. The positive pole usually has a red plastic cap on it in my experience.

The multimeter in the picture has the probes plugged in to the the 10 Amp current measurement plugs, but the dial is set for 2A. It should be two clicks counter clockwise to be at 10A.

But you shouldn’t be using the current measurement for this, unless you disconnected the battery terminals to measure current. If you measured the battery voltage like this, now the fuse needs to be replaced in the multimeter.

The aluminum foil touching both terminals does cause a short. No connection to ground is needed.

Indicates both battery and charging system are working correctly. Battery isn’t fully charged though, unless it was really cold

Unlike a voltage measurement, which can be done with circuit as-is, an amp measurement is done with the meter connected in series with the circuit, meter is part of the circuit in other words. If you placed the meter probes in amp mode directly across the battery terminals, + to -, that creates a short circuit and would usually blow a fuse in the meter, or possibly damage it. Suggest to describe how you did this amp measurement in more detail. Some higher-end (i.e. more $$$) meters, for amp measurements, they come w/a special gadget attachment, made with magnetic materials, that you clamp around the wire. Measures the magnetic field and from that infers the amperage. Is that the type of amp meter you are using? Suggest to consult your meter’s owners manual for proper way to measure current.

That measurement has to be done with everything connected to be meaningful. Was your battery fully connected at the time?

The measurement needed to get to the bottom of an overnight battery drain is called “parasitic current drain measurement”. Done when truck is parked, keys removed, doors closed, everything off. Suggest to Google that term, should explain how a shop would do it. Anything much over 75 mA indicates a problem. My older Corolla’s parasitic drain for example measures 3 mA. If I then open the door and the dome light turns on, and current increases to 500 mA or more.

Note that is is possible to damage your meter and/or your truck’s electronics if you make a mistake doing this sort of testing.

Hey George, thanks for the detailed reply! That is exactly how I did the amp test searching for a parasitic current drain, and connecting the meter in series with the negative pole. Now, I use the 10A port, and someone said that was incorrect, but I think that all what that does is change the decimal value. With the dial set to 2A I got a reading of 0.0815 (but I am not sure if that is milliamps), but then that number would drop 3 seconds later to 0.05 and about 10 seconds later to 0.003. Please refer to the picture above. Yesterday as I as loading my truck I noticed that my fuel pump was running while the truck was off (keys out) -which could be the fuel pump relay (I replaced the oil pressure switch last summer); but when I got home, the fuel pump was totally off once I turned the track off. I have been disconnecting the battery at night to avoid draining it, and the next morning, the truck starts right up. I am trying to get more info so I can try something during the weekend. Thanks