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Dead battery in morning - Phantom/parasitic electrical draw


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Hi everyone, my 2002 SLS has been running great since I replaced the intake plenum back in April... until now.

I parked the car on Friday after work with no issue and didn't get back into it until Monday morning.

On Monday morning, everything was dead. No power locks, no dome lights, nothing. I didn't think much of it and boosted it. I drove about 10 miles and stopped for 1.5 hours before continuing another 5 miles to work. I had no problem restarting after the short stop.

After work, it was 100% dead again - no power locks, domes, or anything. I boosted it and took the battery for a load test which it passed (10.8V). Started/stopped the engine 5+ times with no issue.

Then I disconnected the battery and ran the negative terminal to ground via a multi-meter. With the key in the off position, the draw started around 3A and dropped to 0.55A within a couple minutes. I realized I had my dashcam plugged into the cigar lighter socket (couldn't reach it from the backseat) so I pulled the cigar lighter relay and draw dropped to 0.11A. This is approximately 3x the "maximum allowable" for this car per AllData, though the stand-by power was still active at this point since I was only able to hold the probes for a few minutes.

For now, I'm disconnecting the battery when not using the car.

The only aftermarket item on this car is a remote starter which was installed by a GM dealership by the previous owner. It still works and I use it most mornings.

I had a similar problem in my previous STS, it ended up being a failed power seat breaker and motor. That was easy to isolate because the breaker was red-hot to the touch. I let the SLS cool over the day today before reconnecting the battery about an hour before home time to see if anything was warm to the touch. Nothing was (unsurprising due to the low current).

I've got a couple of questions:

- What is the proper way to proceed with isolating the parasitic load

- Where would an aftermarket remote starter typically be installed and/or fused to the car (I'd like to disconnect it to see if that solves the problem.

Thanks for your help!


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...took the battery for a load test which it passed (10.8V).

I would have the battery load tested several more times to be sure the results are consistent.

...the stand-by power was still active at this point since I was only able to hold the probes for a few minutes.

Run that test again with alligator clips on your test leads. The value you want is the current draw after the RAP (Retained Accessory Power) drops out; approximately 10 minutes. A value in the neighborhood of 25 ma is great.

Do not open or close any doors during the test period.

If your draw does fall to ~~ 25 ma, you are chasing mild corrosion/oxidation on ALL battery cables, including to the fuse panels, OR you are back to a questionable battery.

- Where would an aftermarket starter be physically installed and/or fused to the car (I'd like to disconnect it to see if that solves the problem.

The installer will have to answer that question.


Drive your car.

Use your cell phone.


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what you can do old school is connect a test light inline on the negative side of the battery. I have had poor ground issues on the drivers framerail underneath the air filter housing for the PCM.

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Thanks for the ideas guys! JimD - not sure why I didn't think of alligator clips, they worked perfectly... even grabbed onto the negative "pocket" terminal of the battery!

After accessory power shut down, it hovered around 55mA (flickered between 0.05A and 0.06A).This is approximately twice what the Alldata manual says the maximum should be, and nowhere near enough to kill the battery so quickly. I suspect the consumption is so high due to the remote start keeping something active that wouldn't otherwise be.

I ran the workweek disconnecting the battery twice a day and reconnecting. This made me notice how sensitive the connection between negative terminal and the ground wire is (even a moderately tight connection makes the lights flicker)..

After doing finding only a 55mA draw, I thought id leave the battery connected and see how things went. Its been fine since Thursday night, including over 48 hours parked on the weekend. Thinking about it made me realize two additional details I'd noticed but hadn't really thought about before:

1) When attempting a load test, we first started off using the posts under the hood (which are the posts I used to boost my car). We found 0 volts so pulled out the back seat and tested at the battery.

2) The battery in my remote start died over the weekend that the car had problems... it remained dead over the course of Monday (the day it died again at work) and I replaced the battery on Tuesday.

I'm thinking a loose connection may have been the cause of all this... I'm thinking that when it was starting ok later the same day after only minutes of charging may have been due to the heat in the cab. Ever since the first time I disconnected (and properly reconnected the battery), there haven't been any issues.

Thanks for the replies, and I'll update this thread if the problem returns.

Merry Christmas everyone!!

I thought the remote start remote dying could have cuased the first battery death (two-way communication and maybe the car kept trying to send a "success" signal), but that couldn't explain the second death the same day.


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