Battery Management System & power discharge leak

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Red Top Engine

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On a day at the beach, my alternator failed last summer. I drove the truck as far to as I could before the battery was completely depleted. It was quite impressive how the BMS (battery management system) categorically shut off non-essential power consuming systems, down to the brake lights, until it couldn't generate more sparks. After replacing both the alternator & AGM battery with new, there truck never maintained a full charge. Reset the BMS system with the GAP tool, no difference. After being idle for three days, and sometimes overnight, the truck would be dead following day. Alternator is generating on average above 13.5- 15v.
How prevalent are the BMS failures on these trucks?
 

DaytonaRS7

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possible you have a faulty battery?

when you say it doesn't maintain a full charge..whats your voltages?
off:
running:
while starting:

FYI, this recently happened to me. same exact scenario except I wasnt at a beach. I replaced alternator only and jumped the battery to get ti started again.
I have not had any charging issues or dead batteries since. whatever your issue is is not normal.
 

Red Top Engine

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The battery is 6 months old. I noticed the starting problem started 3 months after replacing the battery and alternator with a OEM used one. My voltages are as follows:
Off: 9.68
Running: 14.3
While starting: 7.3 (I was lucky to get is started without jumping it this time)

There is a draw on the battery when the truck is off- yet everything is off. I unplugged all external lights, winch, etc.

I suspect a faulty diode in the alternator, so I purchased a brand new alternator from Atlantic British- will see if this makes a difference after install. Other possibility might be the BMS?
 

Michael Gain

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The BMS would set a code and alert you on the driver display as a "charging system fault".

It sounds like a parasitic drain somewhere. Likewise, I've read that leaving the key close to the vehicle may prevent complete shutdown of systems. If you are not locking and moving the key a given distance away during those three days of non-activity, that may be another issue.

I am interested to see what the new alternator does for you.
 

avslash

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9.6 off sounds like a bad battery. Isn't an AGM supposed to be somewhere around 10.9-12 when vehicle is off?

9.6 off sounds very low to me.
 

jlglr4

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My understanding is that, with everything off (no drain on battery), battery should be 12.4v-12.6v (12.6v is fully charged. With everything off, 11.9v is considered discharged. I’d put the battery on a charger, see if you can get it up to 12v. Then have it tested at a shop. After being discharged that far, not sure it can be brought back.

If you’re showing 14.3v while running, seems like the alternator is working.

You say that there is a draw on the battery when everything is off, sounds like that’s the problem. Shouldn’t be anything drawing power when it’s completely shut down.
 

gsxr

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My understanding is that, with everything off (no drain on battery), battery should be 12.4v-12.6v (12.6v is fully charged. With everything off, 11.9v is considered discharged. I’d put the battery on a charger, see if you can get it up to 12v. Then have it tested at a shop. After being discharged that far, not sure it can be brought back.

If you’re showing 14.3v while running, seems like the alternator is working.
All of the above is correct: ^^^



You say that there is a draw on the battery when everything is off, sounds like that’s the problem. Shouldn’t be anything drawing power when it’s completely shut down.
This is also correct. Ideally you measure the amount of current draw, and start removing one fuse at a time, until you find out which item stops the excess draw. Then trace that circuit/component and repair whatever is causing the parasitic draw.

If there is a parasitic draw, you can keep replacing batteries and alternators and the problem will persist.


:(
 

Mart

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I've just replaced my alternator. The only indication that it was failing was the intermittent loss of digital radio reception. That occurred over several months, until the alternator started whining. New alternator and digital radio restored.
 

Mart

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I've just replaced my alternator. The only indication that it was failing was the intermittent loss of digital radio reception. That occurred over several months, until the alternator started whining. New alternator and digital radio restored.
 

jlach993

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I've just replaced my alternator. The only indication that it was failing was the intermittent loss of digital radio reception. That occurred over several months, until the alternator started whining. New alternator and digital radio restored.
I had the exact same situation.....for a few weeks my radio wouldn't pick up the HD signal..then my alternator died a few weeks later. I didn't even realize this until i read your post and put two and two together lol...
 

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