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Old 10-02-2014, 10:16 AM
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Slow Battery Drain

So I've been having an issue with my Jeep that has taken me a while to figure out. I finally solved it this past weekend so I just figured I'd throw the problem and solution up here in case anyone comes across the same issue.

When I let my Jeep sit for longer than 24 hours, the battery would be dead when I went to start it. I tried replacing the battery, that didn't solve it. Obviously there was a really slow battery drain. I took apart the wiring to the flood lights in the front and replaced all of that, but that didn't solve it. I rewired the sound bar, thinking the drain might be there, but that didn't do it either.

Finally, I charged the battery, disconnected the alternator, then let it sit for two days. When I reconnected the alternator, the Jeep started back up with no issue.

Turns out that inside the alternator there is a circuit or something that is slowly draining the battery. I'm going to replace the alternator tonight to be sure but I 'm pretty confident that that was the problem.

Hope this helps someone along the way and they don't have to go about rewiring all of the electric like I did.

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Old 10-03-2014, 01:30 AM   #2
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Alternators have rectifiers (diodes) inside that can go bad and cause a battery drain. They can often be replaced, an automotive electrical specialty or alternator repair shop can normally take care of that issue. I'd do that (have it rebuilt) before buying a cheap alternator from some place like AutoZone.

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Old 10-03-2014, 09:04 PM   #3
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Jerry is 100% correct, get your alternator rebuilt by a reputable shop, the reason the discount shops can afford to give you a discount isn't from selling volume, it's from cost cutting rebuilds.
Did you happen to jump start someone recently? The diodes in an alternator can be damaged if you happen to connect the jumper cables backward.
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Old 10-06-2014, 10:57 AM
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The closest place to me that will fix an alternator is about 45 minutes away. The gas + the cost of the repair would be the same as buying a remanufactured alternator. I just bought an alternator for $86 (after I sent the core back). Jeep is running great now.


And no, I haven't jumpstarted anyone with the Jeep. I've had this problem for a while now and have just been avoiding fixing it by making sure to drive the Jeep once a day. Now with the winter coming around I don't want to run the risk of getting stuck somewhere because of not being able to start it up.
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Old 10-06-2014, 11:09 AM   #5
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Just curious if anyone knows, I know places like Autozone and Advanced Auto can test your battery and alternator with their wheel out testing equipment. Will that show if an alternator has a bad diode? If the diode in the alternator is not bad, what is the best process for finding the source of the drain?
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Old 10-06-2014, 12:52 PM   #6
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Originally Posted by Edge1912 View Post
J If the diode in the alternator is not bad, what is the best process for finding the source of the drain?
Hook an ammeter to your negative battery cable, then pull fuses, one at a time until the amp reading goes away. That will allow you to isolate the circuit, then it's simply a matter of finding what in that circuit is causing it.
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Old 10-06-2014, 12:58 PM   #7
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Hook an ammeter to your negative battery cable, then pull fuses, one at a time until the amp reading goes away. That will allow you to isolate the circuit, then it's simply a matter of finding what in that circuit is causing it.
Thank you - I will try that.
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Old 10-06-2014, 02:27 PM   #8
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Be aware there will always be a small drain on the battery from the PCM and radio.
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Old 10-07-2014, 08:29 AM   #9
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Be aware there will always be a small drain on the battery from the PCM and radio.
That makes sense. This is actually on a non-Jeep that I am having the issue. It is a Van that was my Dad's daily driver until he stopped driving. It is drive a couple of times a month at most, and sometimes the battery is dead when we go out to start it. I have had vehicles in the past that would sit for months at a time and fire right up. If this goes 30 days, it is dead. Since he drove it almost daily, the problem may have always been there, but never an issue since it never had time to full drain down. Now when we need it, seems like we have to jump start it.

I also bought an older truck that has a drain. It dies in just days, so I will have to do the amp check while pulling fuses on it too.

OP - sorry for hijacking the thread - hopefully this adds to the discussion.

As mentioned earlier, Autozone and Advanced Auto can test your battery and alternator with their wheel out testing equipment. Will that show if an alternator has a bad diode? According to them, the entire charging system is good (alt, batt, starter), but if this would not show a bad diode, then it could be the same issue that the OP had... Anyone know if the test shows a bad diode?
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Old 10-07-2014, 09:27 AM   #10
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As you stated, you can check for a parasitic battery drain (search you-tube) with a multimeter. Basically, you hook up the meter then pull and replace fuses one at a time to find the drain. I have a similar issue with a little used second car — I now use carry a Jump-N-Carry to get it started.
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Old 10-07-2014, 10:43 AM   #11
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Originally Posted by Edge1912 View Post
That makes sense. This is actually on a non-Jeep that I am having the issue. It is a Van that was my Dad's daily driver until he stopped driving. It is drive a couple of times a month at most, and sometimes the battery is dead when we go out to start it. I have had vehicles in the past that would sit for months at a time and fire right up. If this goes 30 days, it is dead. Since he drove it almost daily, the problem may have always been there, but never an issue since it never had time to full drain down. Now when we need it, seems like we have to jump start it.

I also bought an older truck that has a drain. It dies in just days, so I will have to do the amp check while pulling fuses on it too.

OP - sorry for hijacking the thread - hopefully this adds to the discussion.

As mentioned earlier, Autozone and Advanced Auto can test your battery and alternator with their wheel out testing equipment. Will that show if an alternator has a bad diode? According to them, the entire charging system is good (alt, batt, starter), but if this would not show a bad diode, then it could be the same issue that the OP had... Anyone know if the test shows a bad diode?
The newer the vehicle, the shorter the length of time it can sit without driving before the various onboard electronics drain the battery. I would first take the battery to a BATTERY SHOP not AutoZone etc. and have them give the battery a "load test" which when done correctly, and this test isn't always done correctly, shows the battery's true state of health.

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