Let's Play "What is making my battery drain?"

New to me 2003 GMC Safari. I use it to haul large objects on the weekends. Otherwise it sits parked. Kept getting a low battery and no start so I started collecting data. Alternator puts out 14v. When charged up the battery is at 12.4 volts. Battery looses about .3 volts/24 hrs. My multimeter in resistor mode says there is an open between the + cable and the - cable. This result is obtained both with the cables off the battery or on. It is also obtained regardless of whether I have the multimeter in the kOhm range or the 200Ohm range. In other words I have checked for both a low resistance short and a high resistance short and both with and without the battery connected and there does not appear to be anything downstream of the battery on the vehicle draining the volts. And yet away they go at about .3 of them every day.

Let's discuss. Go!

Been having the same problem with my ranger that only gets driven a few times a month. After chasing all the wires and fuses, I'm of the opinion that new batteries are just garbage.

I cannot confirm OP's problem, but I can say I've had extremely bad luck with batteries in the last decade. Spend the money.

Connect a test light between the negative cable and the battery. If it lights up start pulling fuses until it goes out. That's your problem circuit. 

Stampie said:

Connect a test light between the negative cable and the battery. If it lights up start pulling fuses until it goes out. That's your problem circuit. 

 does the computer draw power  when not running ?

Stampie said:

Connect a test light between the negative cable and the battery. If it lights up start pulling fuses until it goes out. That's your problem circuit. 

This is the easiest, fastest way to find the problem. 

Put a kill switch right at the positive pole of the battery.  You'll have to open the hood to drive the beast, but that is easier than going through the jumping routine.

I have small battery tenders on everything...

Purple Frog said:

Put a kill switch right at the positive pole of the battery.  You'll have to open the hood to drive the beast, but that is easier than going through the jumping routine.

I have small battery tenders on everything...

Or, you know, actually fix the problem.

What Stampie said is the best way to find it. The ECM will draw a tiny bit but not enough to light the test light. 

That's why you use a light instead of a meter. Anything significant enough to drain the battery will light the test light. 

In reply to californiamilleghia :

It should but not a lot. 

A lot of times it is a door sensor not triggering, and some little courtesy light stays on.   Go out at night and look in through the windows.  

Stampie has the correct cure.  

The test light idea is solid, but for tough cases I've used an ammeter connected in series at a battery terminal.

Never occurred to me to test the resistance of the entire electrical system. Curious to hear other people's thoughts on that

In reply to Stampie :

Approved procedure on and off the flight line.

Before I messed around looking for a draw I'd see if the battery dies while it's disconnected.  Statistically, bad batteries are more common than parasitic draws.

In reply to Mr_Asa :

One day I'll tell you the story of the C130  terminal wire shorting on the panel cover. Of course you pull the panel cover to troubleshoot. Hard to troubleshoot a condition when you remove the cause of the problem to troubleshoot. 

APEowner said:

Before I messed around looking for a draw I'd see if the battery dies while it's disconnected.  Statistically, bad batteries are more common than parasitic draws.

That's where I'm at with the ranger. Used a kill switch for a long time because of the door sensors, finally fixed the door sensors, no more drain at all. Then started the no start again, 7 days-5 days, 2 days. Kill switch went back on, voltage would test good running and not, connected and not, but still, couldn't start the truck again after a day or two of sitting disconnected. 

Just put another battery in today, this one with a manufacture date of January 2020. Haven't hooked it up yet, but hoping it lays long enough to sell the truck. 

going to ask a silly question. How old is the battery?

After pulling all the fuses and still drawing current, (I use an ammeter, not a light), then disconnect the alternator.

Thanks for all the ideas! So you guys who are advocating the light bulb - I guess you're saying that technique is somehow different than checking resistance with the multimeter?! Whelp I'll give it a try! I'm kind of looking forward to learning something new.

And to the other ideas/questions:

There's no small light bulb staying on - I have checked it at night. And the van is equipped with a dome light override which I have on/engaged so that the dome lights don't come on when the doors are open.

Full disclosure - there is an aftermarket head unit with a removable face which I have long ago taken off. There is an aftermarket electric trailer brake unit that was my #1 suspect (until I did the resistance check). There is a small spark when I re-connect the + battery cable - but this is typical IMO because at the very least the ECU/PCM/BCM and any other "brains" in the vehicle will have a small parasitic drain on the battery. Any other vehicle I have worked on has this same small spark when connecting the cables back to the battery but they don't drain down the batt as fast. The battery is an interstate brand and does not have a date code sticker on the top or front which are the only sides I can see without removing the battery. I was kind of hoping someone was going to tell me I just have a failed battery which cannot hold a full charge but I wasn't sure how a battery can self-drain due to an internal problem and again the resistance check should have shown something.

Slippery said:

Stampie said:

Connect a test light between the negative cable and the battery. If it lights up start pulling fuses until it goes out. That's your problem circuit. 

This is the easiest, fastest way to find the problem. 

I do this, except with a multimeter set to measure amps.  You'll always get a wee draw from things like the radio memory.

Anything under about .25A is normal.  Pull the neg cable, put the multimeter between the cable and post.  Pull fuses until you get an obvious drop to around .25A and that is your circuit.  That will narrow it down to the things supplied by that fuse.

Sparkydog said:

Thanks for all the ideas! So you guys who are advocating the light bulb - I guess you're saying that technique is somehow different than checking resistance with the multimeter?! Whelp I'll give it a try! I'm kind of looking forward to learning something new.

 

Checking resistance between the negative and positive doesn't do anything.  You're testing a powered, completed circuit.  You're not looking for ohms, you're looking for amperage 

Testing between the pos and neg cables will always reveal a short because there is always something on; radio, ECM, etc.

If the battery is at 12.4V fully charged, your battery is getting ready to take a dirt nap. Should be around 13.2V-ish fully charged.

This is why I lik my old cars. My 1960s MGs etc. can be left with the battery hooked up over the winter and they start the next Spring.

The modern cars have small parasitic draws for ECM, radio presets etc. that can draw them down enough not to start in 3 -4 weeks (less if the battery is on the way out).

Update: With daylight and my glasses I found the date code for my battery... 2013. So I'm gonna get a new battery and then start doing the light bulb thing. I'm looking for current leaks not resistance values!!

In reply to BoxheadTim :

Where do you find these 13.2 v batteries.   A fully charged battery has always been 12 +/- .5 volts from my long experience.

Anybody ever tested a battery with a hydrometer ?