Mystery Battery Draw While Parked UPDATE

[BFL13]

Update 13 Jan--
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Never know--somebody on here might have an idea what to look for, thanks for any help.

2003 Chev 2500HD LT (so has lots of electrical stuff that works with ignition off) 6L gas.

Problem is the battery voltage goes down too fast while engine off parked overnight. Say 12.6 evening then 12.5 next morning then 12.4 next morning, etc.

In theory you can find a mystery draw by pulling fuses one at a time, but there are a kazillion fuses, so it would be helpful to know some likely suspects as nothing appears to be "on" when left overnight.

I took one cable off the battery inserted meter and confirmed there is a steady 0.74 amp draw. I don't know what is a normal amount but this seems high at 18AH a day.

I had the battery load tested and it was in excellent shape with a 400 amp draw and bounced right back. I charged it up and let it sit and it has no unusual self-discharge after a few days. So it is not the battery, it must be a mystery draw AFAIK.

I cannot relate when this started to anything that happened. Years past ISTR it would sit at about 12.5v for long periods while parked. It has been kept plugged in at home mostly with the camper on so the engine battery has been floating at 13.x volts, so I can't say when this all started. Notice it now with the camper off.

The battery dash light glows dimly with ignition off, but it has done that for 19 years. The dash shift indicator lamp is out, which is fairly new- can't see what gear you are in.

So what are some likely suspects that I could check by pulling their fuses or circuit breakers?

[Dick_B]

We had a low draw from our GPS and camera that we plugged into our 12V socket. When it was cold it was enough to drain down the battery so I had to jump start it. We now try to remember to unplug both overnight.

[BFL13]

Thanks for all the ideas! I can get back to it on Thursday according to the weatherman.

Meanwhile it has been bothering me that the 0.74 amp draw at 18AH a day does not match the daily voltage decline. After three days it is 12.4 and 54AH would have a 100AH battery at 12.1. I don't know the AH of a starting battery, but expect it is more like 50AH --not a clue, so it really ought to be flat dead perhaps. Something not right there.

So it is likely the 0.74 amps is not 24/7. It was mentioned earlier that there is a time lag for everything to shut down so the real draw must be less than that 0.74 to match the voltage decline.

I note that taking the neg cable off the batt to do the amps measurement causes the truck's brain to need a reset for some things once reconnected. Inserting the meter reconnects the brain so it might draw more just then while it recovers its mind.

Gremlins galore in the replies! No way I am letting a garage go gremlin hunting at $100/hr, so if I don't find it, I will live with it and plug in the battery maintainer at home. Off-grid camping more than a few days will need attention--steal from the camper or run the truck engine before it gets down too far.

Anyway, have to wait to get back at it. Thanks everyone for the interest. I will report back when I find out more.

[JRscooby]

Ed_Gee wrote:
It may be tedious but I'd start removing fuses, one at a time, check current draw after each fuse removed ... reinstall the removed fuse and move on.

I have a 1156 lamp that I can clip in place between batt post and the disconnected cable. Watch lamp as you pull/replace fuses.

[Groover]

One of my most puzzling problems was a Ford Taurus with a battery drain. I eventually took it to a dealer and they announced that it was a bad battery and replaced the one it. That battery was fairly new and I did not buy that story so I demanded the old one back. I took it home and put in my 1991 F250 with a motor 2 1/2 times as big. The batter did fine in that truck and was still in it 3 later when I sold it. The Taurus was also doing fine with the Ford battery.

Obviously the old batter was good and just as obviously putting a new battery in the Taurus fixed it. I have no explanation for that.

[2003silverado]

Ron Ananian the car doctor was once talking about a bad switch on a lighted glove compartment door wouldn't turn the light off when the glove compartment was closed.

[Thunderbolt]

Back when my brother had his 03 Silverado he had a similar issue and the dealer eventually found that it was the instrument cluster and once they replaced it the problem was solved. Not saying that is the problem with yours, but it is a possibility.

[KD4UPL]

.74 amps is really high. No wonder your battery dies. My 2009 Suburban has the same problem. The battery would be dead in about 3 days if you didn't drive it. I tried putting my meter in line with the negative and pulling fuses. I could never really get anything to make sense.
When you pull certain fuses and then put them back in it causes the stupid build in "security" function to activate blinking the lights and blaring the horn. This would pull more than my 10 amp DC meter could handle and blow it's fuse so watch out for that.
I got fed up and took it to a mechanic. He had it for several days in his shop with a charger on the battery and his meters on various things. He determined that the rear wiper was partly to blame. I had him just unhook it since I rarely use it. He eventually determined the BCM was waking itself up at random when it shouldn't be and causing all sorts of problems. They replaced the BCM. The whole thing cost me about $1,000. Now the battery will last about 7 to 9 days before dying. That's a tremendous improvement but obviously still not quite right. I'm dong throwing time and money at it. Otherwise it's a great vehicle that I like.
My plan is to get a small battery maintainer and mount it under the hood with the cord hanging out the grill like a diesel. I'll just plug it in if I'm not going to drive it.

[Grit_dog]

BobsYourUncle wrote:
Don't rule out the alternator.

While it may appear fine, charge well etc, a bad diode in the rectifier bridge can cause an undetectable "leakage".

I had that once in an old car. The battery would run flat after sitting a few days. I had a dickens of a time figuring it out until I disconnected the alternator and found no drain with it unplugged, and the main battery wire removed. Took it apart, replaced the rectifier assembly - end of problem.

^This is worth checking out. Or rodent damage?

[Grit_dog]

jdc1 wrote:
BC is VERY cold. Would the severe cold weather be doing it? Loads? Memory in computers and radio. Do you have an alarm you turn on? That's another parasitic load.

Yeah, Victoria is in the +40s every day and night in the current forecast, you know sea level, right on the water....And the OP said it's raining out...

[jdc1]

BC is VERY cold. Would the severe cold weather be doing it? Loads? Memory in computers and radio. Do you have an alarm you turn on? That's another parasitic load.

[BFL13]

Lots of good info I didn't know, thanks! More ideas welcome.

On that last one, I can use longer leads on my meter with clamps to insert between the neg post and the neg wire terminal, passed out under the hood with the hood down so I can read the meter (10 amp limit type) from outside.

Raining out now, so will wait on that. Also to check what our 2015 van has for a draw to compare with that 0.74 amp the truck has.

Worst case I can leave it plugged in on a battery maintainer like I do with the engine batt in the Class C. The truck is ok to drive around during the day, battery stays up. Just can't leave it parked for a few days anymore.

[ktmrfs]

there is one VERY important detail about car battery draw with ignition off.

THE VEHICLE GOES THROUGH A SHUTDOWN PROCEDURE ONCE IGNITION IS TURNED OFF. THAT PROCEDURE TAKES TIME AND IS SPECIFIC ON WHAT IS GOING ON.

Trying to measure battery draw before shutdown has actually occurred is IMHO a way to go down a rabbit hole.

So. First, it usually takes 20 minutes or so before it is in full shutdown so checking draw before that is pretty much useless.
Next, for the shutdown to start it usually requires that key is out of ignition, ALL doors, HOOD, trunk, Windows are closed........ get the picture on the next issue.... how to I measure current w/o access to the battery.....

[BobsYourUncle]

Don't rule out the alternator.

While it may appear fine, charge well etc, a bad diode in the rectifier bridge can cause an undetectable "leakage".

I had that once in an old car. The battery would run flat after sitting a few days. I had a dickens of a time figuring it out until I disconnected the alternator and found no drain with it unplugged, and the main battery wire removed. Took it apart, replaced the rectifier assembly - end of problem.

[pianotuna]

How old is the battery?

[otrfun]

A clamp-on DC ammeter may make your troubleshooting a bit more efficient. Some will read down to .1 - .2a relatively accurately and will allow you to check current on a number of wires/cables very quickly. I've troubleshot similar problems as yours and was able to find the source of the problem with just a couple of random wire/cable checks with a clamp-on.

Also, don't know about your Chevy, but when you open the hood or door on our Ram, it temporarily activates portions of the BCM with a several amp load. This load disappears after 5-10 min. Just something to keep in mind so you don't find yourself wasting time chasing phantom draws.

Good luck!