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Battery drain question

1K views 22 replies 6 participants last post by  Newtons3 
#1 ·
So i have a battery drain somewhere and I'm using a multi meter to narrow down my problem from what i have read from other forums is I unhook the negative cable, put the multi meter on the cable and the other one to the negative side battery post, it should tell me a number meaning i have something still drawing power when the jeep is off. my issue is when i hook it up i get a reading of -0.12 but it only stays on the screen for about 12 seconds not long enough for me to pull a fuse and see if it goes down. anyone else have this problem or have any ideas or opinions? i'll try to post a picture of the screen,
 

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#2 ·
You are going to have a parasitic load on the battery when the vehicle is off. The memory for all of your circuits, clocks, etc. do have some measurable electrical load.

Aside from that, you now have a base draw. Pull a fuse and retest. Then pull another. I would also recommend starting with disconnecting the alternator. When you see a change in value, you have found some of the draw. Don't forget accessories like added radios, lights, chargers, etc. which are wired directly to the power source.

My order of disconnection would be:
1. Alternator
2. Any accessories going to the battery or direct power source
3. Radio fuse
4. Interior lighting fuse
5. Dash display fuse
From there it's a crapshoot.

Also, make certain the top of your battery is clean. How fast is it pulling your battery down? How old is your battery? What type/size is your battery?
 
#3 ·
its a year old, and is 550 Cold cranking amps, if i let it sit over night it still starts but very slow crank, after 2 days it will cranks about 2 times then click.. i had it tested at advance auto parts, they did a load test and said it was good,, when i use the multi meter on the battery i got a reading of 13.0 Volts, i started the jeep and turned everything on a/c, headlights, radio, lightbar pretty much everything i could and checked the battery again and it read 12.7 volts, from what i've read thats pretty good and if my alternator was bad it would drop significantly but it didnt.
 
#10 ·
I question any parts store's ability to diagnose a battery.
When you use the multi meter to test battery voltage..... is this running or shut down? Is this after sitting for a while or with a surface charge on it? If the Jeep id running, and you turn headlights, A/C, "and pretty much everything" on, you should not see voltage that low. You should see a voltage rise while running and charging to somewhat over 13 volts. The actual figure will depend on several factors, but 12.7 is definitely too low. ?Your alternator should have no problem supplying all current necessary to operate everything on your Jeep AND charge the battery sufficiently.
If your alternator was bad it would not necessarily drop significantly. If your diodes are bad in your alternator, it CAN charge properly and then drain the battery while sitting. The Alternator CAN also charge at partial rated current. It CAN also struggle with any charging. I would be looking for voltage between 13.5 and 14.4 to indicate a healthy system. The proper way to test the alternator is by using an inductive clamp on the alternator lead to test for current output while monitoring system voltage. Simple battery tests using a typical 125A-175A load are inconclusive and don't show much unless there is severe failure. A carbon pile load and again, an inductive pickup, monitoring system voltage for 30-60 seconds with a follow-up charge and retest would be necessary to really test the battery.

Just GUESSING....shooting from the hip, based on what I think I'm interpreting from what you've written. Your battery voltage at rest seems high, possibly from a sulphated battery or such. It seems that your alternator is not cranking out enough current, but that could be either part affecting the other.
 
#7 ·
i'm confused as to why the .12 volt shows for a bit then goes to full zero

the parasitic drain should continue to show all the time; the meter shouldn't go to full zero
I get that you will have a peak at .12 for a bit when you reconnect the battery, but it should drop to say .08 or something after the initial load

Are you sure you have the meter set to a range that will show hundreds of a volt? it isn't rounding .04 to 0 for example?
 
#13 ·
From your picture, you have the meter set on the right setting, and you've got your probes plugged in right (the red one in the 10A hole is the important part).

You should be touching/connecting the black probe to the battery ground post and the red probe to the battery cable that you disconnected from the battery ground post. The idea is that the current flows through the meter on it's way back to the negative battery post. Is that how you're connecting it? Also, I usually put a 7.5A fuse inline with the red probe, so if something is drawing over that, it blows up that fuse instead of blowing up the meter. If you're connecting it across the battery terminals, that's not going to do anything useful (except maybe trip an automatic circuit breaker in your meter at best, blow a fuse inside the meter or blow up the current sensing circuit in the meter at worst).

It should read something (positive I would hope), provided you've got a radio with memory settings or other things. If it drops back to zero, there's no draw. Turn on the dome light (or maybe the parking lights but not the headlights) and check your meter again. With the dome light on, you should see two things, light from the dome light (obviously) and a number on the meter. If the light is shining and there's no draw, you aren't checking the right battery (do you have two?) If it drops to zero when you turn off the light, then there is no draw (less than .01A or 10mA) with the light off.

You get a small draw (0.12A or 120mA) when you connect the meter, and it goes away after a few seconds. That's kind of strange.
 
#14 ·
so i went out to check it and with my key off i turn the dome lights on and it jumped up to 2.45, when i turned the dome lights off it dropped to 0.12 then down to 0.00, with the key forward i did the same thing with the headlights it went up to 4.55, i turn them off it drops to 0.12 then to 0.00, I even tried to wiggle my key back and forth thinking maybe it was slightly going into the accessory position and it stayed at 0.00. for the record i have the positive cable still hooked to the battery, i have the negative cable off, with the red probe on the cable, and the black probe on the negative battery post, when ive tested it ive had the key in the off position, is this the right way? if this info is correct then does it mean i dont have a parasitic draw? and maybe my alternator is the culprit?
 
#16 ·
You've learned several things here.

  1. You have your meter hooked up correctly and it's working
  2. Your dome light draws 2.45A
  3. Your headlights draw 4.55A
  4. You have a 120mA draw for a few seconds, then 0 (technically, less than 0.01A/10mA) draw when it's sitting with everything turned off. No parasitic "drain" on the battery.
While #2 and #3 might not sound very interesting, they confirm #1 and #4.

Now, about "and maybe my alternator is the culprit?" You've only described your testing, not the symptoms of what's wrong with your Jeep, and you haven't said anything about other tests (at least not in the opening post).

To diagnose further, let's start with the basics.

  • What specifically is the issue you're trying to "fix" here?
  • What other test(s) have you done besides verifying that there's no significant "drain" on your battery when the thing is shut off?
also would it make a difference if i tried the same test with the positive cable? or would it all be the same?
No difference. The current has to make the complete circuit. It's safer to play on the negative terminal because you don't have to worry about any of your wires or probes (or alligator clips or whatever) touching the body or frame (grounding out). If you test on the positive cable, you have to be very careful you don't touch something to the body or frame, it will arc and short out and might weld itself to whatever it touches. I always try to avoid playing with unfused power from an automotive battery. There's no knowledge to be gained, and it's not worth the risk IMO.
 
#18 ·
My symptoms are if I let it sit over night it slow cranks but will start, by the 2nd day its dead, it will slow crank twice then click, this is the only test i have done so far because i figured i had a parasitic draw from something which was causing the battery to drain quickly
 
#19 ·
Is the electrolyte level in the battery good? Have you pulled the caps and checked?

Sounds like the battery is bad and is only holding a small "surface charge." If the battery tests good (shows 500+ CCA on a modern electronic tester), then start looking at starter wiring. Disconnect the negative battery cable before working on the wiring for the starter. If the battery is in the circuit, you will weld a wrench to the starter electrical post if you cross the wrench to ground. Also look at all the ground issues I mentioned.

What's the voltage across the battery posts as soon as you shut it off? And what voltage is showing after a day or two, when you're having the problem? It should be fully charged (around 13.x volts) just after you shut off the engine after a reasonable driving distance (10 miles or more). And the voltage shouldn't drop much at all over a two day period with it shut off.

An alternator issue will cause the battery to not fully charge, but then you wouldn't see 13.x volts on the battery. If the alternator is actually draining the battery while the thing is shut off, the ammeter test you did would show that drain. That's not happening.
 
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